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diff --git a/package/aufs2-util/src/aufs.in.5 b/package/aufs2-util/src/aufs.in.5 deleted file mode 100644 index 0cbb14487..000000000 --- a/package/aufs2-util/src/aufs.in.5 +++ /dev/null @@ -1,1684 +0,0 @@ -.\".so aufs.tmac -. -.eo -.de TQ -.br -.ns -.TP \$1 -.. -.de Bu -.IP \(bu 4 -.. -.ec -.\" end of macro definitions -. -.\" ---------------------------------------------------------------------- -.TH aufs 5 \*[AUFS_VERSION] Linux "Linux Aufs User's Manual" -.SH NAME -aufs \- advanced multi layered unification filesystem. version \*[AUFS_VERSION] - -.\" ---------------------------------------------------------------------- -.SH DESCRIPTION -Aufs is a stackable unification filesystem such as Unionfs, which unifies -several directories and provides a merged single directory. -In the early days, aufs was entirely re-designed and re-implemented -Unionfs Version 1.x series. After -many original ideas, approaches and improvements, it -becomes totally different from Unionfs while keeping the basic features. -See Unionfs Version 1.x series for the basic features. -Recently, Unionfs Version 2.x series begin taking some of same -approaches to aufs's. - -.\" ---------------------------------------------------------------------- -.SH MOUNT OPTIONS -At mount-time, the order of interpreting options is, -.RS -.Bu -simple flags, except xino/noxino and udba=inotify -.Bu -branches -.Bu -xino/noxino -.Bu -udba=inotify -.RE - -At remount-time, -the options are interpreted in the given order, -e.g. left to right. -.RS -.Bu -create or remove -whiteout-base(\*[AUFS_WH_BASE]) and -whplink-dir(\*[AUFS_WH_PLINKDIR]) if necessary -.RE -. -.TP -.B br:BRANCH[:BRANCH ...] (dirs=BRANCH[:BRANCH ...]) -Adds new branches. -(cf. Branch Syntax). - -Aufs rejects the branch which is an ancestor or a descendant of another -branch. It is called overlapped. When the branch is loopback-mounted -directory, aufs also checks the source fs-image file of loopback -device. If the source file is a descendant of another branch, it will -be rejected too. - -After mounting aufs or adding a branch, if you move a branch under -another branch and make it descendant of another branch, aufs will not -work correctly. -. -.TP -.B [ add | ins ]:index:BRANCH -Adds a new branch. -The index begins with 0. -Aufs creates -whiteout-base(\*[AUFS_WH_BASE]) and -whplink-dir(\*[AUFS_WH_PLINKDIR]) if necessary. - -If there is the same named file on the lower branch (larger index), -aufs will hide the lower file. -You can only see the highest file. -You will be confused if the added branch has whiteouts (including -diropq), they may or may not hide the lower entries. -.\" It is recommended to make sure that the added branch has no whiteout. - -Even if a process have once mapped a file by mmap(2) with MAP_SHARED -and the same named file exists on the lower branch, -the process still refers the file on the lower(hidden) -branch after adding the branch. -If you want to update the contents of a process address space after -adding, you need to restart your process or open/mmap the file again. -.\" Usually, such files are executables or shared libraries. -(cf. Branch Syntax). -. -.TP -.B del:dir -Removes a branch. -Aufs does not remove -whiteout-base(\*[AUFS_WH_BASE]) and -whplink-dir(\*[AUFS_WH_PLINKDIR]) automatically. -For example, when you add a RO branch which was unified as RW, you -will see whiteout-base or whplink-dir on the added RO branch. - -If a process is referencing the file/directory on the deleting branch -(by open, mmap, current working directory, etc.), aufs will return an -error EBUSY. -. -.TP -.B mod:BRANCH -Modifies the permission flags of the branch. -Aufs creates or removes -whiteout-base(\*[AUFS_WH_BASE]) and/or -whplink-dir(\*[AUFS_WH_PLINKDIR]) if necessary. - -If the branch permission is been changing `rw' to `ro', and a process -is mapping a file by mmap(2) -.\" with MAP_SHARED -on the branch, the process may or may not -be able to modify its mapped memory region after modifying branch -permission flags. -Additioanlly when you enable CONFIG_IMA (in linux-2.6.30 and later), IMA -may produce some wrong messages. But this is equivalent when the -filesystem is changed `ro' in emergency. -(cf. Branch Syntax). -. -.TP -.B append:BRANCH -equivalent to `add:(last index + 1):BRANCH'. -(cf. Branch Syntax). -. -.TP -.B prepend:BRANCH -equivalent to `add:0:BRANCH.' -(cf. Branch Syntax). -. -.TP -.B xino=filename -Use external inode number bitmap and translation table. -When CONFIG_AUFS_EXPORT is enabled, external inode generation table too. -It is set to -<FirstWritableBranch>/\*[AUFS_XINO_FNAME] by default, or -\*[AUFS_XINO_DEFPATH]. -Comma character in filename is not allowed. - -The files are created per an aufs and per a branch filesystem, and -unlinked. So you -cannot find this file, but it exists and is read/written frequently by -aufs. -(cf. External Inode Number Bitmap, Translation Table and Generation Table). - -If you enable CONFIG_SYSFS, the path of xino files are not shown in -/proc/mounts (and /etc/mtab), instead it is shown in -<sysfs>/fs/aufs/si_<id>/xi_path. -Otherwise, it is shown in /proc/mounts unless it is not the default -path. -. -.TP -.B noxino -Stop using external inode number bitmap and translation table. - -If you use this option, -Some applications will not work correctly. -.\" And pseudo link feature will not work after the inode cache is -.\" shrunk. -(cf. External Inode Number Bitmap, Translation Table and Generation Table). -. -.TP -.B trunc_xib -Truncate the external inode number bitmap file. The truncation is done -automatically when you delete a branch unless you do not specify -`notrunc_xib' option. -(cf. External Inode Number Bitmap, Translation Table and Generation Table). -. -.TP -.B notrunc_xib -Stop truncating the external inode number bitmap file when you delete -a branch. -(cf. External Inode Number Bitmap, Translation Table and Generation Table). -. -.TP -.B create_policy | create=CREATE_POLICY -.TQ -.B copyup_policy | copyup | cpup=COPYUP_POLICY -Policies to select one among multiple writable branches. The default -values are `create=tdp' and `cpup=tdp'. -link(2) and rename(2) systemcalls have an exception. In aufs, they -try keeping their operations in the branch where the source exists. -(cf. Policies to Select One among Multiple Writable Branches). -. -.TP -.B verbose | v -Print some information. -Currently, it is only busy file (or inode) at deleting a branch. -. -.TP -.B noverbose | quiet | q | silent -Disable `verbose' option. -This is default value. -. -.TP -.B sum -df(1)/statfs(2) returns the total number of blocks and inodes of -all branches. -Note that there are cases that systemcalls may return ENOSPC, even if -df(1)/statfs(2) shows that aufs has some free space/inode. -. -.TP -.B nosum -Disable `sum' option. -This is default value. -. -.TP -.B dirwh=N -Watermark to remove a dir actually at rmdir(2) and rename(2). - -If the target dir which is being removed or renamed (destination dir) -has a huge number of whiteouts, i.e. the dir is empty logically but -physically, the cost to remove/rename the single -dir may be very high. -It is -required to unlink all of whiteouts internally before issuing -rmdir/rename to the branch. -To reduce the cost of single systemcall, -aufs renames the target dir to a whiteout-ed temporary name and -invokes a pre-created -kernel thread to remove whiteout-ed children and the target dir. -The rmdir/rename systemcall returns just after kicking the thread. - -When the number of whiteout-ed children is less than the value of -dirwh, aufs remove them in a single systemcall instead of passing -another thread. -This value is ignored when the branch is NFS. -The default value is \*[AUFS_DIRWH_DEF]. -.\" . -.\" .TP -.\" .B rdcache=N -. -.TP -.B rdblk=N -Specifies a size of internal VDIR block which is allocated at a time in -byte. -The VDIR block will be allocated several times when necessary. If your -directory has millions of files, you may want to expand this size. -The default value is defined as \*[AUFS_RDBLK_DEF]. -The size has to be lager than NAME_MAX (usually 255) and kmalloc\-able -(the maximum limit depends on your system. at least 128KB is available -for every system). -Whenever you can reset the value to default by specifying rdblk=def. -(cf. Virtual or Vertical Directory Block). -. -.TP -.B rdhash=N -Specifies a size of internal VDIR hash table which is used to compare -the file names under the same named directory on multiple branches. -The VDIR hash table will be allocated in readdir(3)/getdents(2), -rmdir(2) and rename(2) for the existing target directory. If your -directory has millions of files, you may want to expand this size. -The default value is defined as \*[AUFS_RDHASH_DEF]. -The size has to be lager than zero, and it will be multiplied by 4 or 8 -(for 32\-bit and 64\-bit respectively, currently). The result must be -kmalloc\-able -(the maximum limit depends on your system. at least 128KB is available -for every system). -Whenever you can reset the value to default by specifying rdhash=def. -(cf. Virtual or Vertical Directory Block). -. -.TP -.B plink -.TQ -.B noplink -Specifies to use `pseudo link' feature or not. -The default is `plink' which means use this feature. -(cf. Pseudo Link) -. -.TP -.B clean_plink -Removes all pseudo-links in memory. -In order to make pseudo-link permanent, use -`auplink' utility just before one of these operations, -unmounting aufs, -using `ro' or `noplink' mount option, -deleting a branch from aufs, -adding a branch into aufs, -or changing your writable branch as readonly. -If you installed both of /sbin/mount.aufs and /sbin/umount.aufs, and your -mount(8) and umount(8) support them, -`auplink' utility will be executed automatically and flush pseudo-links. -(cf. Pseudo Link) -. -.TP -.B udba=none | reval | inotify -Specifies the level of UDBA (User's Direct Branch Access) test. -(cf. User's Direct Branch Access and Inotify Limitation). -. -.TP -.B diropq=whiteouted | w | always | a -Specifies whether mkdir(2) and rename(2) dir case make the created directory -`opaque' or not. -In other words, to create `\*[AUFS_WH_DIROPQ]' under the created or renamed -directory, or not to create. -When you specify diropq=w or diropq=whiteouted, aufs will not create -it if the -directory was not whiteouted or opaqued. If the directory was whiteouted -or opaqued, the created or renamed directory will be opaque. -When you specify diropq=a or diropq==always, aufs will always create -it regardless -the directory was whiteouted/opaqued or not. -The default value is diropq=w, it means not to create when it is unnecessary. -If you define CONFIG_AUFS_COMPAT at aufs compiling time, the default will be -diropq=a. -You need to consider this option if you are planning to add a branch later -since `diropq' affects the same named directory on the added branch. -. -.TP -.B warn_perm -.TQ -.B nowarn_perm -Adding a branch, aufs will issue a warning about uid/gid/permission of -the adding branch directory, -when they differ from the existing branch's. This difference may or -may not impose a security risk. -If you are sure that there is no problem and want to stop the warning, -use `nowarn_perm' option. -The default is `warn_perm' (cf. DIAGNOSTICS). -. -.TP -.B shwh -.TQ -.B noshwh -By default (noshwh), aufs doesn't show the whiteouts and -they just hide the same named entries in the lower branches. The -whiteout itself also never be appeared. -If you enable CONFIG_AUFS_SHWH and specify `shwh' option, aufs -will show you the name of whiteouts -with keeping its feature to hide the lowers. -Honestly speaking, I am rather confused with this `visible whiteouts.' -But a user who originally requested this feature wrote a nice how-to -document about this feature. See Tips file in the aufs CVS tree. - -.\" ---------------------------------------------------------------------- -.SH Module Parameters -.TP -.B nwkq=N -The number of kernel thread named \*[AUFS_WKQ_NAME]. - -Those threads stay in the system while the aufs module is loaded, -and handle the special I/O requests from aufs. -The default value is \*[AUFS_NWKQ_DEF]. - -The special I/O requests from aufs include a part of copy-up, lookup, -directory handling, pseudo-link, xino file operations and the -delegated access to branches. -For example, Unix filesystems allow you to rmdir(2) which has no write -permission bit, if its parent directory has write permission bit. In aufs, the -removing directory may or may not have whiteout or `dir opaque' mark as its -child. And aufs needs to unlink(2) them before rmdir(2). -Therefore aufs delegates the actual unlink(2) and rmdir(2) to another kernel -thread which has been created already and has a superuser privilege. - -If you enable CONFIG_SYSFS, you can check this value through -<sysfs>/module/aufs/parameters/nwkq. - -. -.TP -.B brs=1 | 0 -Specifies to use the branch path data file under sysfs or not. - -If the number of your branches is large or their path is long -and you meet the limitation of mount(8) ro /etc/mtab, you need to -enable CONFIG_SYSFS and set aufs module parameter brs=1. - -When this parameter is set as 1, aufs does not show `br:' (or dirs=) -mount option through /proc/mounts (and /etc/mtab). So you can -keep yourself from the page limitation of -mount(8) or /etc/mtab. -Aufs shows branch paths through <sysfs>/fs/aufs/si_XXX/brNNN. -Actually the file under sysfs has also a size limitation, but I don't -think it is harmful. - -There is one more side effect in setting 1 to this parameter. -If you rename your branch, the branch path written in /etc/mtab will be -obsoleted and the future remount will meet some error due to the -unmatched parameters (Remember that mount(8) may take the options from -/etc/mtab and pass them to the systemcall). -If you set 1, /etc/mtab will not hold the branch path and you will not -meet such trouble. On the other hand, the entries for the -branch path under sysfs are generated dynamically. So it must not be obsoleted. -But I don't think users want to rename branches so often. - -If CONFIG_SYSFS is disable, this parameter is always set to 0. -. -.TP -.B sysrq=key -Specifies MagicSysRq key for debugging aufs. -You need to enable both of CONFIG_MAGIC_SYSRQ and CONFIG_AUFS_DEBUG. -Currently this is for developers only. -The default is `a'. -. -.TP -.B debug= 0 | 1 -Specifies disable(0) or enable(1) debug print in aufs. -This parameter can be changed dynamically. -You need to enable CONFIG_AUFS_DEBUG. -Currently this is for developers only. -The default is `0' (disable). - -.\" ---------------------------------------------------------------------- -.SH Entries under Sysfs and Debugfs -See linux/Documentation/ABI/*/{sys,debug}fs-aufs. - -.\" ---------------------------------------------------------------------- -.SH Branch Syntax -.TP -.B dir_path[ =permission [ + attribute ] ] -.TQ -.B permission := rw | ro | rr -.TQ -.B attribute := wh | nolwh -dir_path is a directory path. -The keyword after `dir_path=' is a -permission flags for that branch. -Comma, colon and the permission flags string (including `=')in the path -are not allowed. - -Any filesystem can be a branch, But some are not accepted such like -sysfs, procfs and unionfs. -If you specify such filesystems as an aufs branch, aufs will return an error -saying it is unsupported. - -Cramfs in linux stable release has strange inodes and it makes aufs -confused. For example, -.nf -$ mkdir -p w/d1 w/d2 -$ > w/z1 -$ > w/z2 -$ mkcramfs w cramfs -$ sudo mount -t cramfs -o ro,loop cramfs /mnt -$ find /mnt -ls - 76 1 drwxr-xr-x 1 jro 232 64 Jan 1 1970 /mnt - 1 1 drwxr-xr-x 1 jro 232 0 Jan 1 1970 /mnt/d1 - 1 1 drwxr-xr-x 1 jro 232 0 Jan 1 1970 /mnt/d2 - 1 1 -rw-r--r-- 1 jro 232 0 Jan 1 1970 /mnt/z1 - 1 1 -rw-r--r-- 1 jro 232 0 Jan 1 1970 /mnt/z2 -.fi - -All these two directories and two files have the same inode with one -as their link count. Aufs cannot handle such inode correctly. -Currently, aufs involves a tiny workaround for such inodes. But some -applications may not work correctly since aufs inode number for such -inode will change silently. -If you do not have any empty files, empty directories or special files, -inodes on cramfs will be all fine. - -A branch should not be shared as the writable branch between multiple -aufs. A readonly branch can be shared. - -The maximum number of branches is configurable at compile time (127 by -default). - -When an unknown permission or attribute is given, aufs sets ro to that -branch silently. - -.SS Permission -. -.TP -.B rw -Readable and writable branch. Set as default for the first branch. -If the branch filesystem is mounted as readonly, you cannot set it `rw.' -.\" A filesystem which does not support link(2) and i_op\->setattr(), for -.\" example FAT, will not be used as the writable branch. -. -.TP -.B ro -Readonly branch and it has no whiteouts on it. -Set as default for all branches except the first one. Aufs never issue -both of write operation and lookup operation for whiteout to this branch. -. -.TP -.B rr -Real readonly branch, special case of `ro', for natively readonly -branch. Assuming the branch is natively readonly, aufs can optimize -some internal operation. For example, if you specify `udba=inotify' -option, aufs does not set inotify for the things on rr branch. -Set by default for a branch whose fs-type is either `iso9660', -`cramfs' or `romfs' (and `squashfs' for linux\-2.6.29 and later). - -When your branch exists on slower device and you have some -capacity on your hdd, you may want to try ulobdev tool in ULOOP sample. -It can cache the contents of the real devices on another faster device, -so you will be able to get the better access performance. -The ulobdev tool is for a generic block device, and the ulohttp is for a -filesystem image on http server. -If you want to spin down your hdd to save the -battery life or something, then you may want to use ulobdev to save the -access to the hdd, too. -See $AufsCVS/sample/uloop in detail. - -.SS Attribute -. -.TP -.B wh -Readonly branch and it has/might have whiteouts on it. -Aufs never issue write operation to this branch, but lookup for whiteout. -Use this as `<branch_dir>=ro+wh'. -. -.TP -.B nolwh -Usually, aufs creates a whiteout as a hardlink on a writable -branch. This attributes prohibits aufs to create the hardlinked -whiteout, including the source file of all hardlinked whiteout -(\*[AUFS_WH_BASE].) -If you do not like a hardlink, or your writable branch does not support -link(2), then use this attribute. -But I am afraid a filesystem which does not support link(2) natively -will fail in other place such as copy-up. -Use this as `<branch_dir>=rw+nolwh'. -Also you may want to try `noplink' mount option, while it is not recommended. - -.\" .SS FUSE as a branch -.\" A FUSE branch needs special attention. -.\" The struct fuse_operations has a statfs operation. It is OK, but the -.\" parameter is struct statvfs* instead of struct statfs*. So almost -.\" all user\-space implementation will call statvfs(3)/fstatvfs(3) instead of -.\" statfs(2)/fstatfs(2). -.\" In glibc, [f]statvfs(3) issues [f]statfs(2), open(2)/read(2) for -.\" /proc/mounts, -.\" and stat(2) for the mountpoint. With this situation, a FUSE branch will -.\" cause a deadlock in creating something in aufs. Here is a sample -.\" scenario, -.\" .\" .RS -.\" .\" .IN -10 -.\" .Bu -.\" create/modify a file just under the aufs root dir. -.\" .Bu -.\" aufs acquires a write\-lock for the parent directory, ie. the root dir. -.\" .Bu -.\" A library function or fuse internal may call statfs for a fuse branch. -.\" The create=mfs mode in aufs will surely call statfs for each writable -.\" branches. -.\" .Bu -.\" FUSE in kernel\-space converts and redirects the statfs request to the -.\" user\-space. -.\" .Bu -.\" the user\-space statfs handler will call [f]statvfs(3). -.\" .Bu -.\" the [f]statvfs(3) in glibc will access /proc/mounts and issue -.\" stat(2) for the mountpoint. But those require a read\-lock for the aufs -.\" root directory. -.\" .Bu -.\" Then a deadlock occurs. -.\" .\" .RE 1 -.\" .\" .IN -.\" -.\" In order to avoid this deadlock, I would suggest not to call -.\" [f]statvfs(3) from fuse. Here is a sample code to do this. -.\" .nf -.\" struct statvfs stvfs; -.\" -.\" main() -.\" { -.\" statvfs(..., &stvfs) -.\" or -.\" fstatvfs(..., &stvfs) -.\" stvfs.f_fsid = 0 -.\" } -.\" -.\" statfs_handler(const char *path, struct statvfs *arg) -.\" { -.\" struct statfs stfs -.\" -.\" memcpy(arg, &stvfs, sizeof(stvfs)) -.\" -.\" statfs(..., &stfs) -.\" or -.\" fstatfs(..., &stfs) -.\" -.\" arg->f_bfree = stfs.f_bfree -.\" arg->f_bavail = stfs.f_bavail -.\" arg->f_ffree = stfs.f_ffree -.\" arg->f_favail = /* any value */ -.\" } -.\" .fi - -.\" ---------------------------------------------------------------------- -.SH External Inode Number Bitmap, Translation Table and Generation Table (xino) -Aufs uses one external bitmap file and one external inode number -translation table files per an aufs and per a branch -filesystem by default. -Additionally when CONFIG_AUFS_EXPORT is enabled, one external inode -generation table is added. -The bitmap (and the generation table) is for recycling aufs inode number -and the others -are a table for converting an inode number on a branch to -an aufs inode number. The default path -is `first writable branch'/\*[AUFS_XINO_FNAME]. -If there is no writable branch, the -default path -will be \*[AUFS_XINO_DEFPATH]. -.\" A user who executes mount(8) needs the privilege to create xino -.\" file. - -If you enable CONFIG_SYSFS, the path of xino files are not shown in -/proc/mounts (and /etc/mtab), instead it is shown in -<sysfs>/fs/aufs/si_<id>/xi_path. -Otherwise, it is shown in /proc/mounts unless it is not the default -path. - -Those files are always opened and read/write by aufs frequently. -If your writable branch is on flash memory device, it is recommended -to put xino files on other than flash memory by specifying `xino=' -mount option. - -The -maximum file size of the bitmap is, basically, the amount of the -number of all the files on all branches divided by 8 (the number of -bits in a byte). -For example, on a 4KB page size system, if you have 32,768 (or -2,599,968) files in aufs world, -then the maximum file size of the bitmap is 4KB (or 320KB). - -The -maximum file size of the table will -be `max inode number on the branch x size of an inode number'. -For example in 32bit environment, - -.nf -$ df -i /branch_fs -/dev/hda14 2599968 203127 2396841 8% /branch_fs -.fi - -and /branch_fs is an branch of the aufs. When the inode number is -assigned contiguously (without `hole'), the maximum xino file size for -/branch_fs will be 2,599,968 x 4 bytes = about 10 MB. But it might not be -allocated all of disk blocks. -When the inode number is assigned discontinuously, the maximum size of -xino file will be the largest inode number on a branch x 4 bytes. -Additionally, the file size is limited to LLONG_MAX or the s_maxbytes -in filesystem's superblock (s_maxbytes may be smaller than -LLONG_MAX). So the -support-able largest inode number on a branch is less than -2305843009213693950 (LLONG_MAX/4\-1). -This is the current limitation of aufs. -On 64bit environment, this limitation becomes more strict and the -supported largest inode number is less than LLONG_MAX/8\-1. - -The xino files are always hidden, i.e. removed. So you cannot -do `ls \-l xino_file'. -If you enable CONFIG_DEBUG_FS, you can check these information through -<debugfs>/aufs/<si_id>/{xib,xi[0-9]*,xigen}. xib is for the bitmap file, -xi0 ix for the first branch, and xi1 is for the next. xigen is for the -generation table. -xib and xigen are in the format of, - -.nf -<blocks>x<block size> <file size> -.fi - -Note that a filesystem usually has a -feature called pre-allocation, which means a number of -blocks are allocated automatically, and then deallocated -silently when the filesystem thinks they are unnecessary. -You do not have to be surprised the sudden changes of the number of -blocks, when your filesystem which xino files are placed supports the -pre-allocation feature. - -The rests are hidden xino file information in the format of, - -.nf -<file count>, <blocks>x<block size> <file size> -.fi - -If the file count is larger than 1, it means some of your branches are -on the same filesystem and the xino file is shared by them. -Note that the file size may not be equal to the actual consuming blocks -since xino file is a sparse file, i.e. a hole in a file which does not -consume any disk blocks. - -Once you unmount aufs, the xino files for that aufs are totally gone. -It means that the inode number is not permanent across umount or -shutdown. - -The xino files should be created on the filesystem except NFS. -If your first writable branch is NFS, you will need to specify xino -file path other than NFS. -Also if you are going to remove the branch where xino files exist or -change the branch permission to readonly, you need to use xino option -before del/mod the branch. - -The bitmap file can be truncated. -For example, if you delete a branch which has huge number of files, -many inode numbers will be recycled and the bitmap will be truncated -to smaller size. Aufs does this automatically when a branch is -deleted. -You can truncate it anytime you like if you specify `trunc_xib' mount -option. But when the accessed inode number was not deleted, nothing -will be truncated. -If you do not want to truncate it (it may be slow) when you delete a -branch, specify `notrunc_xib' after `del' mount option. - -If you do not want to use xino, use noxino mount option. Use this -option with care, since the inode number may be changed silently and -unexpectedly anytime. -For example, -rmdir failure, recursive chmod/chown/etc to a large and deep directory -or anything else. -And some applications will not work correctly. -.\" When the inode number has been changed, your system -.\" can be crazy. -If you want to change the xino default path, use xino mount option. - -After you add branches, the persistence of inode number may not be -guaranteed. -At remount time, cached but unused inodes are discarded. -And the newly appeared inode may have different inode number at the -next access time. The inodes in use have the persistent inode number. - -When aufs assigned an inode number to a file, and if you create the -same named file on the upper branch directly, then the next time you -access the file, aufs may assign another inode number to the file even -if you use xino option. -Some applications may treat the file whose inode number has been -changed as totally different file. - -.\" ---------------------------------------------------------------------- -.SH Pseudo Link (hardlink over branches) -Aufs supports `pseudo link' which is a logical hard-link over -branches (cf. ln(1) and link(2)). -In other words, a copied-up file by link(2) and a copied-up file which was -hard-linked on a readonly branch filesystem. - -When you have files named fileA and fileB which are -hardlinked on a readonly branch, if you write something into fileA, -aufs copies-up fileA to a writable branch, and write(2) the originally -requested thing to the copied-up fileA. On the writable branch, -fileA is not hardlinked. -But aufs remembers it was hardlinked, and handles fileB as if it existed -on the writable branch, by referencing fileA's inode on the writable -branch as fileB's inode. - -Once you unmount aufs, the plink info for that aufs kept in memory are totally -gone. -It means that the pseudo-link is not permanent. -If you want to make plink permanent, try `auplink' utility just before -one of these operations, -unmounting your aufs, -using `ro' or `noplink' mount option, -deleting a branch from aufs, -adding a branch into aufs, -or changing your writable branch to readonly. - -This utility will reproduces all real hardlinks on a writable branch by linking -them, and removes pseudo-link info in memory and temporary link on the -writable branch. -Since this utility access your branches directly, you cannot hide them by -`mount \-\-bind /tmp /branch' or something. - -If you are willing to rebuild your aufs with the same branches later, you -should use auplink utility before you umount your aufs. -If you installed both of /sbin/mount.aufs and /sbin/umount.aufs, and your -mount(8) and umount(8) support them, -`auplink' utility will be executed automatically and flush pseudo-links. - -.nf -# auplink /your/aufs/root flush -# umount /your/aufs/root -or -# auplink /your/aufs/root flush -# mount -o remount,mod:/your/writable/branch=ro /your/aufs/root -or -# auplink /your/aufs/root flush -# mount -o remount,noplink /your/aufs/root -or -# auplink /your/aufs/root flush -# mount -o remount,del:/your/aufs/branch /your/aufs/root -or -# auplink /your/aufs/root flush -# mount -o remount,append:/your/aufs/branch /your/aufs/root -.fi - -The plinks are kept both in memory and on disk. When they consumes too much -resources on your system, you can use the `auplink' utility at anytime and -throw away the unnecessary pseudo-links in safe. - -Additionally, the `auplink' utility is very useful for some security reasons. -For example, when you have a directory whose permission flags -are 0700, and a file who is 0644 under the 0700 directory. Usually, -all files under the 0700 directory are private and no one else can see -the file. But when the directory is 0711 and someone else knows the 0644 -filename, he can read the file. - -Basically, aufs pseudo-link feature creates a temporary link under the -directory whose owner is root and the permission flags are 0700. -But when the writable branch is NFS, aufs sets 0711 to the directory. -When the 0644 file is pseudo-linked, the temporary link, of course the -contents of the file is totally equivalent, will be created under the -0711 directory. The filename will be generated by its inode number. -While it is hard to know the generated filename, someone else may try peeping -the temporary pseudo-linked file by his software tool which may try the name -from one to MAX_INT or something. -In this case, the 0644 file will be read unexpectedly. -I am afraid that leaving the temporary pseudo-links can be a security hole. -It makes sense to execute `auplink /your/aufs/root flush' -periodically, when your writable branch is NFS. - -When your writable branch is not NFS, or all users are careful enough to set 0600 -to their private files, you do not have to worry about this issue. - -If you do not want this feature, use `noplink' mount option. - -.SS The behaviours of plink and noplink -This sample shows that the `f_src_linked2' with `noplink' option cannot follow -the link. - -.nf -none on /dev/shm/u type aufs (rw,xino=/dev/shm/rw/.aufs.xino,br:/dev/shm/rw=rw:/dev/shm/ro=ro) -$ ls -li ../r?/f_src_linked* ./f_src_linked* ./copied -ls: ./copied: No such file or directory -15 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ../ro/f_src_linked -15 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ../ro/f_src_linked2 -22 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ./f_src_linked -22 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ./f_src_linked2 -$ echo abc >> f_src_linked -$ cp f_src_linked copied -$ ls -li ../r?/f_src_linked* ./f_src_linked* ./copied -15 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ../ro/f_src_linked -15 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ../ro/f_src_linked2 -36 -rw-r--r-- 2 jro jro 6 Dec 22 11:03 ../rw/f_src_linked -53 -rw-r--r-- 1 jro jro 6 Dec 22 11:03 ./copied -22 -rw-r--r-- 2 jro jro 6 Dec 22 11:03 ./f_src_linked -22 -rw-r--r-- 2 jro jro 6 Dec 22 11:03 ./f_src_linked2 -$ cmp copied f_src_linked2 -$ - -none on /dev/shm/u type aufs (rw,xino=/dev/shm/rw/.aufs.xino,noplink,br:/dev/shm/rw=rw:/dev/shm/ro=ro) -$ ls -li ../r?/f_src_linked* ./f_src_linked* ./copied -ls: ./copied: No such file or directory -17 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ../ro/f_src_linked -17 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ../ro/f_src_linked2 -23 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ./f_src_linked -23 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ./f_src_linked2 -$ echo abc >> f_src_linked -$ cp f_src_linked copied -$ ls -li ../r?/f_src_linked* ./f_src_linked* ./copied -17 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ../ro/f_src_linked -17 -rw-r--r-- 2 jro jro 2 Dec 22 11:03 ../ro/f_src_linked2 -36 -rw-r--r-- 1 jro jro 6 Dec 22 11:03 ../rw/f_src_linked -53 -rw-r--r-- 1 jro jro 6 Dec 22 11:03 ./copied -23 -rw-r--r-- 2 jro jro 6 Dec 22 11:03 ./f_src_linked -23 -rw-r--r-- 2 jro jro 6 Dec 22 11:03 ./f_src_linked2 -$ cmp copied f_src_linked2 -cmp: EOF on f_src_linked2 -$ -.fi - -.\" -.\" If you add/del a branch, or link/unlink the pseudo-linked -.\" file on a branch -.\" directly, aufs cannot keep the correct link count, but the status of -.\" `pseudo-linked.' -.\" Those files may or may not keep the file data after you unlink the -.\" file on the branch directly, especially the case of your branch is -.\" NFS. - -If you add a branch which has fileA or fileB, aufs does not follow the -pseudo link. The file on the added branch has no relation to the same -named file(s) on the lower branch(es). -If you use noxino mount option, pseudo link will not work after the -kernel shrinks the inode cache. - -This feature will not work for squashfs before version 3.2 since its -inode is tricky. -When the inode is hardlinked, squashfs inodes has the same inode -number and correct link count, but the inode memory object is -different. Squashfs inodes (before v3.2) are generated for each, even -they are hardlinked. - -.\" ---------------------------------------------------------------------- -.SH User's Direct Branch Access (UDBA) -UDBA means a modification to a branch filesystem manually or directly, -e.g. bypassing aufs. -While aufs is designed and implemented to be safe after UDBA, -it can make yourself and your aufs confused. And some information like -aufs inode will be incorrect. -For example, if you rename a file on a branch directly, the file on -aufs may -or may not be accessible through both of old and new name. -Because aufs caches various information about the files on -branches. And the cache still remains after UDBA. - -Aufs has a mount option named `udba' which specifies the test level at -access time whether UDBA was happened or not. -. -.TP -.B udba=none -Aufs trusts the dentry and the inode cache on the system, and never -test about UDBA. With this option, aufs runs fastest, but it may show -you incorrect data. -Additionally, if you often modify a branch -directly, aufs will not be able to trace the changes of inodes on the -branch. It can be a cause of wrong behaviour, deadlock or anything else. - -It is recommended to use this option only when you are sure that -nobody access a file on a branch. -It might be difficult for you to achieve real `no UDBA' world when you -cannot stop your users doing `find / \-ls' or something. -If you really want to forbid all of your users to UDBA, here is a trick -for it. -With this trick, users cannot see the -branches directly and aufs runs with no problem, except `auplink' utility. -But if you are not familiar with aufs, this trick may make -yourself confused. - -.nf -# d=/tmp/.aufs.hide -# mkdir $d -# for i in $branches_you_want_to_hide -> do -> mount -n --bind $d $i -> done -.fi - -When you unmount the aufs, delete/modify the branch by remount, or you -want to show the hidden branches again, unmount the bound -/tmp/.aufs.hide. - -.nf -# umount -n $branches_you_want_to_unbound -.fi - -If you use FUSE filesystem as an aufs branch which supports hardlink, -you should not set this option, since FUSE makes inode objects for -each hardlinks (at least in linux\-2.6.23). When your FUSE filesystem -maintains them at link/unlinking, it is equivalent -to `direct branch access' for aufs. - -. -.TP -.B udba=reval -Aufs tests only the existence of the file which existed. If -the existed file was removed on the branch directly, aufs -discard the cache about the file and -re-lookup it. So the data will be updated. -This test is at minimum level to keep the performance and ensure the -existence of a file. -This is default and aufs runs still fast. - -This rule leads to some unexpected situation, but I hope it is -harmless. Those are totally depends upon cache. Here are just a few -examples. -. -.RS -.Bu -If the file is cached as negative or -not-existed, aufs does not test it. And the file is still handled as -negative after a user created the file on a branch directly. If the -file is not cached, aufs will lookup normally and find the file. -. -.Bu -When the file is cached as positive or existed, and a user created the -same named file directly on the upper branch. Aufs detects the cached -inode of the file is still existing and will show you the old (cached) -file which is on the lower branch. -. -.Bu -When the file is cached as positive or existed, and a user renamed the -file by rename(2) directly. Aufs detects the inode of the file is -still existing. You may or may not see both of the old and new files. -Todo: If aufs also tests the name, we can detect this case. -.RE - -If your outer modification (UDBA) is rare and you can ignore the -temporary and minor differences between virtual aufs world and real -branch filesystem, then try this mount option. -. -.TP -.B udba=inotify -Aufs sets `inotify' to all the accessed directories on its branches -and receives the event about the dir and its children. It consumes -resources, cpu and memory. And I am afraid that the performance will be -hurt, but it is most strict test level. -There are some limitations of linux inotify, see also Inotify -Limitation. -So it is recommended to leave udba default option usually, and set it -to inotify by remount when you need it. - -When a user accesses the file which was notified UDBA before, the cached data -about the file will be discarded and aufs re-lookup it. So the data will -be updated. -When an error condition occurs between UDBA and aufs operation, aufs -will return an error, including EIO. -To use this option, you need to enable CONFIG_INOTIFY and -CONFIG_AUFS_UDBA_INOTIFY. - -To rename/rmdir a directory on a branch directory may reveal the same named -directory on the lower branch. Aufs tries re-lookuping the renamed -directory and the revealed directory and assigning different inode -number to them. But the inode number including their children can be a -problem. The inode numbers will be changed silently, and -aufs may produce a warning. If you rename a directory repeatedly and -reveal/hide the lower directory, then aufs may confuse their inode -numbers too. It depends upon the system cache. - -When you make a directory in aufs and mount other filesystem on it, -the directory in aufs cannot be removed expectedly because it is a -mount point. But the same named directory on the writable branch can -be removed, if someone wants. It is just an empty directory, instead -of a mount point. -Aufs cannot stop such direct rmdir, but produces a warning about it. - -If the pseudo-linked file is hardlinked or unlinked on the branch -directly, its inode link count in aufs may be incorrect. It is -recommended to flush the pseudo-links by auplink script. - -.\" ---------------------------------------------------------------------- -.SH Linux Inotify Limitation -Unfortunately, current inotify (linux\-2.6.18) has some limitations, -and aufs must derive it. - -.SS IN_ATTRIB, updating atime -When a file/dir on a branch is accessed directly, the inode atime (access -time, cf. stat(2)) may or may not be updated. In some cases, inotify -does not fire this event. So the aufs inode atime may remain old. - -.SS IN_ATTRIB, updating nlink -When the link count of a file on a branch is incremented by link(2) -directly, -inotify fires IN_CREATE to the parent -directory, but IN_ATTRIB to the file. So the aufs inode nlink may -remain old. - -.SS IN_DELETE, removing file on NFS -When a file on a NFS branch is deleted directly, inotify may or may -not fire -IN_DELETE event. It depends upon the status of dentry -(DCACHE_NFSFS_RENAMED flag). -In this case, the file on aufs seems still exists. Aufs and any user can see -the file. - -.SS IN_IGNORED, deleted rename target -When a file/dir on a branch is unlinked by rename(2) directly, inotify -fires IN_IGNORED which means the inode is deleted. Actually, in some -cases, the inode survives. For example, the rename target is linked or -opened. In this case, inotify watch set by aufs is removed by VFS and -inotify. -And aufs cannot receive the events anymore. So aufs may show you -incorrect data about the file/dir. - -.\" ---------------------------------------------------------------------- -.SH Virtual or Vertical Directory Block (VDIR) -In order to provide the merged view of file listing, aufs builds -internal directory block on memory. For readdir, aufs performs readdir() -internally for each dir on branches, merges their entries with -eliminating the whiteout\-ed ones, and sets it to the opened file (dir) -object. So the file object has its entry list until it is closed. The -entry list will be updated when the file position is zero (by -rewinddir(3)) and becomes obsoleted. - -Some people may call it can be a security hole or invite DoS attack -since the opened and once readdir\-ed dir (file object) holds its entry -list and becomes a pressure for system memory. But I would say it is similar -to files under /proc or /sys. The virtual files in them also holds a -memory page (generally) while they are opened. When an idea to reduce -memory for them is introduced, it will be applied to aufs too. - -The dynamically allocated memory block for the name of entries has a -unit of \*[AUFS_RDBLK_DEF] bytes by default. -During building dir blocks, aufs creates hash list (hashed and divided by -\*[AUFS_RDHASH_DEF] by default) and judging whether -the entry is whiteouted by its upper branch or already listed. - -These values are suitable for normal environments. But you may have -millions of files or very long filenames under a single directory. For -such cases, you may need to customize these values by specifying rdblk= -and rdhash= aufs mount options. - -For instance, there are 97 files under my /bin, and the total name -length is 597 bytes. - -.nf -$ \\ls -1 /bin | wc - 97 97 597 -.fi - -Strictly speaking, 97 end\-of\-line codes are -included. But it is OK since aufs VDIR also stores the name length in 1 -byte. In this case, you do not need to customize the default values. 597 bytes -filenames will be stored in 2 VDIR memory blocks (597 < -\*[AUFS_RDBLK_DEF] x 2). -And 97 filenames are distributed among \*[AUFS_RDHASH_DEF] lists, so one -list will point 4 names in average. To judge the names is whiteouted or -not, the number of comparison will be 4. 2 memory allocations -and 4 comparison costs low (even if the directory is opened for a long -time). So you do not need to customize. - -If your directory has millions of files, the you will need to specify -rdblk= and rdhash=. - -.nf -$ ls -U /mnt/rotating-rust | wc -l -1382438 -.fi - -In this case, assuming the average length of filenames is 6, in order to -get better time performance I would -recommend to set $((128*1024)) or $((64*1024)) for rdblk, and -$((8*1024)) or $((4*1024)) for rdhash. -You can change these values of the active aufs mount by "mount -o -remount". - -This customization is not for -reducing the memory space, but for reducing time for the number of memory -allocation and the name comparison. The larger value is faster, in -general. Of course, you will need system memory. This is a generic -"time\-vs\-space" problem. - -.\" ---------------------------------------------------------------------- -.SH Copy On Write, or aufs internal copyup and copydown -Every stackable filesystem which implements copy\-on\-write supports the -copyup feature. The feature is to copy a file/dir from the lower branch -to the upper internally. When you have one readonly branch and one -upper writable branch, and you append a string to a file which exists on -the readonly branch, then aufs will copy the file from the readonly -branch to the writable branch with its directory hierarchy. It means one -write(2) involves several logical/internal mkdir(2), creat(2), read(2), -write(2) and close(2) systemcalls -before the actual expected write(2) is performed. Sometimes it may take -a long time, particularly when the file is very large. -If CONFIG_AUFS_DEBUG is enabled, aufs produces a message saying `copying -a large file.' - -You may see the message when you change the xino file path or -truncate the xino/xib files. Sometimes those files can be large and may -take a long time to handle them. - -.\" ---------------------------------------------------------------------- -.SH Policies to Select One among Multiple Writable Branches -Aufs has some policies to select one among multiple writable branches -when you are going to write/modify something. There are two kinds of -policies, one is for newly create something and the other is for -internal copy-up. -You can select them by specifying mount option `create=CREATE_POLICY' -or `cpup=COPYUP_POLICY.' -These policies have no meaning when you have only one writable -branch. If there is some meaning, it must hurt the performance. - -.SS Exceptions for Policies -In every cases below, even if the policy says that the branch where a -new file should be created is /rw2, the file will be created on /rw1. -. -.Bu -If there is a readonly branch with `wh' attribute above the -policy-selected branch and the parent dir is marked as opaque, -or the target (creating) file is whiteouted on the ro+wh branch, then -the policy will be ignored and the target file will be created on the -nearest upper writable branch than the ro+wh branch. -.RS -.nf -/aufs = /rw1 + /ro+wh/diropq + /rw2 -/aufs = /rw1 + /ro+wh/wh.tgt + /rw2 -.fi -.RE -. -.Bu -If there is a writable branch above the policy-selected branch and the -parent dir is marked as opaque or the target file is whiteouted on the -branch, then the policy will be ignored and the target file will be -created on the highest one among the upper writable branches who has -diropq or whiteout. In case of whiteout, aufs removes it as usual. -.RS -.nf -/aufs = /rw1/diropq + /rw2 -/aufs = /rw1/wh.tgt + /rw2 -.fi -.RE -. -.Bu -link(2) and rename(2) systemcalls are exceptions in every policy. -They try selecting the branch where the source exists as possible since -copyup a large file will take long time. If it can't be, ie. the -branch where the source exists is readonly, then they will follow the -copyup policy. -. -.Bu -There is an exception for rename(2) when the target exists. -If the rename target exists, aufs compares the index of the branches -where the source and the target are existing and selects the higher -one. If the selected branch is readonly, then aufs follows the copyup -policy. - -.SS Policies for Creating -. -.TP -.B create=tdp | top\-down\-parent -Selects the highest writable branch where the parent dir exists. If -the parent dir does not exist on a writable branch, then the internal -copyup will happen. The policy for this copyup is always `bottom-up.' -This is the default policy. -. -.TP -.B create=rr | round\-robin -Selects a writable branch in round robin. When you have two writable -branches and creates 10 new files, 5 files will be created for each -branch. -mkdir(2) systemcall is an exception. When you create 10 new directories, -all are created on the same branch. -. -.TP -.B create=mfs[:second] | most\-free\-space[:second] -Selects a writable branch which has most free space. In order to keep -the performance, you can specify the duration (`second') which makes -aufs hold the index of last selected writable branch until the -specified seconds expires. The first time you create something in aufs -after the specified seconds expired, aufs checks the amount of free -space of all writable branches by internal statfs call -and the held branch index will be updated. -The default value is \*[AUFS_MFS_SECOND_DEF] seconds. -. -.TP -.B create=mfsrr:low[:second] -Selects a writable branch in most-free-space mode first, and then -round-robin mode. If the selected branch has less free space than the -specified value `low' in bytes, then aufs re-tries in round-robin mode. -.\" `G', `M' and `K' (case insensitive) can be followed after `low.' Or -Try an arithmetic expansion of shell which is defined by POSIX. -For example, $((10 * 1024 * 1024)) for 10M. -You can also specify the duration (`second') which is equivalent to -the `mfs' mode. -. -.TP -.B create=pmfs[:second] -Selects a writable branch where the parent dir exists, such as tdp -mode. When the parent dir exists on multiple writable branches, aufs -selects the one which has most free space, such as mfs mode. - -.SS Policies for Copy-Up -. -.TP -.B cpup=tdp | top\-down\-parent -Equivalent to the same named policy for create. -This is the default policy. -. -.TP -.B cpup=bup | bottom\-up\-parent -Selects the writable branch where the parent dir exists and the branch -is nearest upper one from the copyup-source. -. -.TP -.B cpup=bu | bottom\-up -Selects the nearest upper writable branch from the copyup-source, -regardless the existence of the parent dir. - -.\" ---------------------------------------------------------------------- -.SH Exporting Aufs via NFS -Aufs is supporting NFS-exporting. -Since aufs has no actual block device, you need to add NFS `fsid' option at -exporting. Refer to the manual of NFS about the detail of this option. - -There are some limitations or requirements. -.RS -.Bu -The branch filesystem must support NFS-exporting. -.Bu -NFSv2 is not supported. When you mount the exported aufs from your NFS -client, you will need to some NFS options like v3 or nfsvers=3, -especially if it is nfsroot. -.Bu -If the size of the NFS file handle on your branch filesystem is large, -aufs will -not be able to handle it. The maximum size of NFSv3 file -handle for a filesystem is 64 bytes. Aufs uses 24 bytes for 32bit -system, plus 12 bytes for 64bit system. The rest is a room for a file -handle of a branch filesystem. -.Bu -The External Inode Number Bitmap, Translation Table and Generation Table -(xino) is -required since NFS file -handle is based upon inode number. The mount option `xino' is enabled -by default. -The external inode generation table and its debugfs entry -(<debugfs>/aufs/si_*/xigen) is created when CONFIG_AUFS_EXPORT is -enabled even if you don't export aufs actually. -The size of the external inode generation table grows only, never be -truncated. You might need to pay attention to the free space of the -filesystem where xino files are placed. By default, it is the first -writable branch. -.Bu -The branch filesystems must be accessible, which means `not hidden.' -It means you need to `mount \-\-move' when you use initramfs and -switch_root(8), or chroot(8). -.RE - -.\" ---------------------------------------------------------------------- -.SH Dentry and Inode Caches -If you want to clear caches on your system, there are several tricks -for that. If your system ram is low, -try `find /large/dir \-ls > /dev/null'. -It will read many inodes and dentries and cache them. Then old caches will be -discarded. -But when you have large ram or you do not have such large -directory, it is not effective. - -If you want to discard cache within a certain filesystem, -try `mount \-o remount /your/mntpnt'. Some filesystem may return an error of -EINVAL or something, but VFS discards the unused dentry/inode caches on the -specified filesystem. - -.\" ---------------------------------------------------------------------- -.SH Compatible/Incompatible with Unionfs Version 1.x Series -If you compile aufs with \-DCONFIG_AUFS_COMPAT, dirs= option and =nfsro -branch permission flag are available. They are interpreted as -br: option and =ro flags respectively. - `debug', `delete', `imap' options are ignored silently. When you -compile aufs without \-DCONFIG_AUFS_COMPAT, these three options are -also ignored, but a warning message is issued. - -Ignoring `delete' option, and to keep filesystem consistency, aufs tries -writing something to only one branch in a single systemcall. It means -aufs may copyup even if the copyup-src branch is specified as writable. -For example, you have two writable branches and a large regular file -on the lower writable branch. When you issue rename(2) to the file on aufs, -aufs may copyup it to the upper writable branch. -If this behaviour is not what you want, then you should rename(2) it -on the lower branch directly. - -And there is a simple shell -script `unionctl' under sample subdirectory, which is compatible with -unionctl(8) in -Unionfs Version 1.x series, except \-\-query action. -This script executes mount(8) with `remount' option and uses -add/del/mod aufs mount options. -If you are familiar with Unionfs Version 1.x series and want to use unionctl(8), you can -try this script instead of using mount \-o remount,... directly. -Aufs does not support ioctl(2) interface. -This script is highly depending upon mount(8) in -util\-linux\-2.12p package, and you need to mount /proc to use this script. -If your mount(8) version differs, you can try modifying this -script. It is very easy. -The unionctl script is just for a sample usage of aufs remount -interface. - -Aufs uses the external inode number bitmap and translation table by -default. - -The default branch permission for the first branch is `rw', and the -rest is `ro.' - -The whiteout is for hiding files on lower branches. Also it is applied -to stop readdir going lower branches. -The latter case is called `opaque directory.' Any -whiteout is an empty file, it means whiteout is just an mark. -In the case of hiding lower files, the name of whiteout is -`\*[AUFS_WH_PFX]<filename>.' -And in the case of stopping readdir, the name is -`\*[AUFS_WH_PFX]\*[AUFS_WH_PFX].opq' or -`\*[AUFS_WH_PFX]__dir_opaque.' The name depends upon your compile -configuration -CONFIG_AUFS_COMPAT. -.\" All of newly created or renamed directory will be opaque. -All whiteouts are hardlinked, -including `<writable branch top dir>/\*[AUFS_WH_BASE].' - -The hardlink on an ordinary (disk based) filesystem does not -consume inode resource newly. But in linux tmpfs, the number of free -inodes will be decremented by link(2). It is recommended to specify -nr_inodes option to your tmpfs if you meet ENOSPC. Use this option -after checking by `df \-i.' - -When you rmdir or rename-to the dir who has a number of whiteouts, -aufs rename the dir to the temporary whiteouted-name like -`\*[AUFS_WH_PFX]<dir>.<random hex>.' Then remove it after actual operation. -cf. mount option `dirwh.' - -.\" ---------------------------------------------------------------------- -.SH Incompatible with an Ordinary Filesystem -stat(2) returns the inode info from the first existence inode among -the branches, except the directory link count. -Aufs computes the directory link count larger than the exact value usually, in -order to keep UNIX filesystem semantics, or in order to shut find(1) mouth up. -The size of a directory may be wrong too, but it has to do no harm. -The timestamp of a directory will not be updated when a file is -created or removed under it, and it was done on a lower branch. - -The test for permission bits has two cases. One is for a directory, -and the other is for a non-directory. In the case of a directory, aufs -checks the permission bits of all existing directories. It means you -need the correct privilege for the directories including the lower -branches. -The test for a non-directory is more simple. It checks only the -topmost inode. - -statfs(2) returns the information of the first branch info except -namelen when `nosum' is specified (the default). The namelen is -decreased by the whiteout prefix length. And the block size may differ -from st_blksize which is obtained by stat(2). - -Remember, seekdir(3) and telldir(3) are not defined in POSIX. They may -not work as you expect. Try rewinddir(3) or re-open the dir. - -The whiteout prefix (\*[AUFS_WH_PFX]) is reserved on all branches. Users should -not handle the filename begins with this prefix. -In order to future whiteout, the maximum filename length is limited by -the longest value \- \*[AUFS_WH_PFX_LEN]. It may be a violation of POSIX. - -If you dislike the difference between the aufs entries in /etc/mtab -and /proc/mounts, and if you are using mount(8) in util\-linux package, -then try ./mount.aufs utility. Copy the script to /sbin/mount.aufs. -This simple utility tries updating -/etc/mtab. If you do not care about /etc/mtab, you can ignore this -utility. -Remember this utility is highly depending upon mount(8) in -util\-linux\-2.12p package, and you need to mount /proc. - -Since aufs uses its own inode and dentry, your system may cache huge -number of inodes and dentries. It can be as twice as all of the files -in your union. -It means that unmounting or remounting readonly at shutdown time may -take a long time, since mount(2) in VFS tries freeing all of the cache -on the target filesystem. - -When you open a directory, aufs will open several directories -internally. -It means you may reach the limit of the number of file descriptor. -And when the lower directory cannot be opened, aufs will close all the -opened upper directories and return an error. - -The sub-mount under the branch -of local filesystem -is ignored. -For example, if you have mount another filesystem on -/branch/another/mntpnt, the files under `mntpnt' will be ignored by aufs. -It is recommended to mount the sub-mount under the mounted aufs. -For example, - -.nf -# sudo mount /dev/sdaXX /ro_branch -# d=another/mntpnt -# sudo mount /dev/sdbXX /ro_branch/$d -# mkdir -p /rw_branch/$d -# sudo mount -t aufs -o br:/rw_branch:/ro_branch none /aufs -# sudo mount -t aufs -o br:/rw_branch/${d}:/ro_branch/${d} none /aufs/another/$d -.fi - -There are several characters which are not allowed to use in a branch -directory path and xino filename. See detail in Branch Syntax and Mount -Option. - -The file-lock which means fcntl(2) with F_SETLK, F_SETLKW or F_GETLK, flock(2) -and lockf(3), is applied to virtual aufs file only, not to the file on a -branch. It means you can break the lock by accessing a branch directly. -TODO: check `security' to hook locks, as inotify does. - -The I/O to the named pipe or local socket are not handled by aufs, even -if it exists in aufs. After the reader and the writer established their -connection if the pipe/socket are copied-up, they keep using the old one -instead of the copied-up one. - -The fsync(2) and fdatasync(2) systemcalls return 0 which means success, even -if the given file descriptor is not opened for writing. -I am afraid this behaviour may violate some standards. Checking the -behaviour of fsync(2) on ext2, aufs decided to return success. - -If you want to use disk-quota, you should set it up to your writable -branch since aufs does not have its own block device. - -When your aufs is the root directory of your system, and your system -tells you some of the filesystem were not unmounted cleanly, try these -procedure when you shutdown your system. -.nf -# mount -no remount,ro / -# for i in $writable_branches -# do mount -no remount,ro $i -# done -.fi -If your xino file is on a hard drive, you also need to specify -`noxino' option or `xino=/your/tmpfs/xino' at remounting root -directory. - -To rename(2) directory may return EXDEV even if both of src and tgt -are on the same aufs. When the rename-src dir exists on multiple -branches and the lower dir has child(ren), aufs has to copyup all his -children. It can be recursive copyup. Current aufs does not support -such huge copyup operation at one time in kernel space, instead -produces a warning and returns EXDEV. -Generally, mv(1) detects this error and tries mkdir(2) and -rename(2) or copy/unlink recursively. So the result is harmless. -If your application which issues rename(2) for a directory does not -support EXDEV, it will not work on aufs. -Also this specification is applied to the case when the src directory -exists on the lower readonly branch and it has child(ren). - -If a sudden accident such like a power failure happens during aufs is -performing, and regular fsck for branch filesystems is completed after -the disaster, you need to extra fsck for aufs writable branches. It is -necessary to check whether the whiteout remains incorrectly or not, -eg. the real filename and the whiteout for it under the same parent -directory. If such whiteout remains, aufs cannot handle the file -correctly. -To check the consistency from the aufs' point of view, you can use a -simple shell script called /sbin/auchk. Its purpose is a fsck tool for -aufs, and it checks the illegal whiteout, the remained -pseudo-links and the remained aufs-temp files. If they are found, the -utility reports you and asks whether to delete or not. -It is recommended to execute /sbin/auchk for every writable branch -filesystem before mounting aufs if the system experienced crash. - - -.\" ---------------------------------------------------------------------- -.SH EXAMPLES -The mount options are interpreted from left to right at remount-time. -These examples -shows how the options are handled. (assuming /sbin/mount.aufs was -installed) - -.nf -# mount -v -t aufs br:/day0:/base none /u -none on /u type aufs (rw,xino=/day0/.aufs.xino,br:/day0=rw:/base=ro) -# mount -v -o remount,\\ - prepend:/day1,\\ - xino=/day1/xino,\\ - mod:/day0=ro,\\ - del:/day0 \\ - /u -none on /u type aufs (rw,xino=/day1/xino,br:/day1=rw:/base=ro) -.fi - -.nf -# mount -t aufs br:/rw none /u -# mount -o remount,append:/ro /u -different uid/gid/permission, /ro -# mount -o remount,del:/ro /u -# mount -o remount,nowarn_perm,append:/ro /u -# -(there is no warning) -.fi - -.\" If you want to expand your filesystem size, aufs may help you by -.\" adding an writable branch. Since aufs supports multiple writable -.\" branches, the old writable branch can be being writable, if you want. -.\" In this example, any modifications to the files under /ro branch will -.\" be copied-up to /new, but modifications to the files under /rw branch -.\" will not. -.\" And the next example shows the modifications to the files under /rw branch -.\" will be copied-up to /new/a. -.\" -.\" Todo: test multiple writable branches policy. cpup=nearest, cpup=exist_parent. -.\" -.\" .nf -.\" # mount -v -t aufs br:/rw:/ro none /u -.\" none on /u type aufs (rw,xino=/rw/.aufs.xino,br:/rw=rw:/ro=ro) -.\" # mkfs /new -.\" # mount -v -o remount,add:1:/new=rw /u -.\" none on /u type aufs (rw,xino=/rw/.aufs.xino,br:/rw=rw:/new=rw:/ro=ro) -.\" .fi -.\" -.\" .nf -.\" # mount -v -t aufs br:/rw:/ro none /u -.\" none on /u type aufs (rw,xino=/rw/.aufs.xino,br:/rw=rw:/ro=ro) -.\" # mkfs /new -.\" # mkdir /new/a new/b -.\" # mount -v -o remount,add:1:/new/b=rw,prepend:/new/a,mod:/rw=ro /u -.\" none on /u type aufs (rw,xino=/rw/.aufs.xino,br:/new/a=rw:/rw=ro:/new/b=rw:/ro=ro) -.\" .fi - -When you use aufs as root filesystem, it is recommended to consider to -exclude some directories. For example, /tmp and /var/log are not need -to stack in many cases. They do not usually need to copyup or to whiteout. -Also the swapfile on aufs (a regular file, not a block device) is not -supported. -In order to exclude the specific dir from aufs, try bind mounting. - -And there is a good sample which is for network booted diskless machines. See -sample/ in detail. - -.\" ---------------------------------------------------------------------- -.SH DIAGNOSTICS -When you add a branch to your union, aufs may warn you about the -privilege or security of the branch, which is the permission bits, -owner and group of the top directory of the branch. -For example, when your upper writable branch has a world writable top -directory, -a malicious user can create any files on the writable branch directly, -like copyup and modify manually. I am afraid it can be a security -issue. - -When you mount or remount your union without \-o ro common mount option -and without writable branch, aufs will warn you that the first branch -should be writable. - -.\" It is discouraged to set both of `udba' and `noxino' mount options. In -.\" this case the inode number under aufs will always be changed and may -.\" reach the end of inode number which is a maximum of unsigned long. If -.\" the inode number reaches the end, aufs will return EIO repeatedly. - -When you set udba other than inotify and change something on your -branch filesystem directly, later aufs may detect some mismatches to -its cache. If it is a critical mismatch, aufs returns EIO. - -When an error occurs in aufs, aufs prints the kernel message with -`errno.' The priority of the message (log level) is ERR or WARNING which -depends upon the message itself. -You can convert the `errno' into the error message by perror(3), -strerror(3) or something. -For example, the `errno' in the message `I/O Error, write failed (\-28)' -is 28 which means ENOSPC or `No space left on device.' - -When CONFIG_AUFS_BR_RAMFS is enabled, you can specify ramfs as an aufs -branch. Since ramfs is simple, it does not set the maximum link count -originally. In aufs, it is very dangerous, particularly for -whiteouts. Finally aufs sets the maximum link count for ramfs. The -value is 32000 which is borrowed from ext2. - - -.\" .SH Current Limitation -. -.\" ---------------------------------------------------------------------- -.\" SYNOPSIS -.\" briefly describes the command or function's interface. For commands, this -.\" shows the syntax of the command and its arguments (including options); bold- -.\" face is used for as-is text and italics are used to indicate replaceable -.\" arguments. Brackets ([]) surround optional arguments, vertical bars (|) sep- -.\" arate choices, and ellipses (...) can be repeated. For functions, it shows -.\" any required data declarations or #include directives, followed by the func- -.\" tion declaration. -. -.\" DESCRIPTION -.\" gives an explanation of what the command, function, or format does. Discuss -.\" how it interacts with files and standard input, and what it produces on -.\" standard output or standard error. Omit internals and implementation -.\" details unless they're critical for understanding the interface. Describe -.\" the usual case; for information on options use the OPTIONS section. If -.\" there is some kind of input grammar or complex set of subcommands, consider -.\" describing them in a separate USAGE section (and just place an overview in -.\" the DESCRIPTION section). -. -.\" RETURN VALUE -.\" gives a list of the values the library routine will return to the caller and -.\" the conditions that cause these values to be returned. -. -.\" EXIT STATUS -.\" lists the possible exit status values or a program and the conditions that -.\" cause these values to be returned. -. -.\" USAGE -.\" describes the grammar of any sublanguage this implements. -. -.\" FILES -.\" lists the files the program or function uses, such as configuration files, -.\" startup files, and files the program directly operates on. Give the full -.\" pathname of these files, and use the installation process to modify the -.\" directory part to match user preferences. For many programs, the default -.\" installation location is in /usr/local, so your base manual page should use -.\" /usr/local as the base. -. -.\" ENVIRONMENT -.\" lists all environment variables that affect your program or function and how -.\" they affect it. -. -.\" SECURITY -.\" discusses security issues and implications. Warn about configurations or -.\" environments that should be avoided, commands that may have security impli- -.\" cations, and so on, especially if they aren't obvious. Discussing security -.\" in a separate section isn't necessary; if it's easier to understand, place -.\" security information in the other sections (such as the DESCRIPTION or USAGE -.\" section). However, please include security information somewhere! -. -.\" CONFORMING TO -.\" describes any standards or conventions this implements. -. -.\" NOTES -.\" provides miscellaneous notes. -. -.\" BUGS -.\" lists limitations, known defects or inconveniences, and other questionable -.\" activities. - -.SH COPYRIGHT -Copyright \(co 2005\-2009 Junjiro R. Okajima - -.SH AUTHOR -Junjiro R. Okajima - -.\" SEE ALSO -.\" lists related man pages in alphabetical order, possibly followed by other -.\" related pages or documents. Conventionally this is the last section. |