Holger Schurig: > > I've read documentation for aufs and there is some note that aufs2 > > utilities are always necessary. > > That's not true. I use a basic aufs2 system on my device and > don't use or even have installed aufs utilities. It can all be > done with "mount -o ...". > > I guess you'll need the utilities only for advanced stuff :-)
aufs2-util is essentially necessary, especially these files. (from the aufs2-util README) ---------------------------------------------------------------------- o /sbin/mount.aufs, /sbin/umount.aufs Helpers for util-linux-ng package. You should NOT invoke them manually. Just install them by "make install". o /sbin/auplink Handles aufs pseudo-link at remount/unmount time. You can invoke it manually at anytime. ---------------------------------------------------------------------- They are always invoked at mount/remount/unmount time. The main purpose of /sbin/mount.aufs is, - maintain /etc/mtab - maintain the aufs pseudo-link (by calling /sbin/auplink) If you don't install /sbin/mount.aufs, then the aufs line in your /etc/mtab will be incorrect, and you may loose the aufs pseudo-link. /sbin/auplink is called by /sbin/umount.aufs too. If you don't know what the aufs pseudo-link is, then refer to the aufs manual in detail. Additional information, (from linux/Documentation/filesystems/aufs/design/02struct.txt) Pseudo-link ---------------------------------------------------------------------- Assume "fileA" exists on the lower readonly branch only and it is hardlinked to "fileB" on the branch. When you write something to fileA, aufs copies-up it to the upper writable branch. Additionally aufs creates a hardlink under the Pseudo-link Directory of the writable branch. The inode of a pseudo-link is kept in aufs super_block as a simple list. If fileB is read after unlinking fileA, aufs returns filedata from the pseudo-link instead of the lower readonly branch. Because the pseudo-link is based upon the inode, to keep the inode number by xino (see above) is important. All the hardlinks under the Pseudo-link Directory of the writable branch should be restored in a proper location later. Aufs provides a utility to do this. The userspace helpers executed at remounting and unmounting aufs by default. ---------------------------------------------------------------------- And http://www.mail-archive.com/[email protected]/msg02639.html If you don't care about /etc/mtab and the pseudo-link, you can uninstall aufs2-util. Otherwise, just install it. aufs2-util contains other useful things. o /usr/bin/auchk Similar to generic fsck. Checks whether a branch is healthy or not from aufs's point of view. o /usr/bin/aubrsync Move files from the upper writable branch to the lower branch. If you use this script with aufs1, then you need to install aufs.shlib to /usr/lib/aufs.shlib. Currently only the 20080211 version is tested for aufs1. The development of this script is sponcered by ASUSTek Computer Inc. (http://www.asus.com/). Kindly they agreed that I keep my aufs work as free software as it has been. o /usr/lib/libau.so A dynamic link library for "readdir(3) in user-space". If you need this , then run "make libau.so install_ulib". And refer to the aufs manual in detail. Generally readdir(3) in libau.so runs faster than readdir in aufs kernel-space, particulary for the huge dir. J. R. Okajima ------------------------------------------------------------------------------ This SF.net email is sponsored by Sprint What will you do first with EVO, the first 4G phone? Visit sprint.com/first -- http://p.sf.net/sfu/sprint-com-first
