UNIONFS(1)

NAME
Unionfs - a unioning file system for Linux

SYNOPSIS
Unionfs is not a command, but rather a file system. This manual page describes additional mount options that Unionfs supports.

mount -t unionfs -o dirs=/branch1[=ro|=rw]:/branch2[=ro|=rw]:...:/branchN[=ro|=rw],[copyup=preserve,currentuser,mounter] none /mnt/unionfs

DESCRIPTION
dirs specifies a colon separated list which directories should compose the union. Additionally, read-only or read-write permissions of the branch can be specified by appending "=ro" or "=rw" to each directory. Directories that come earlier in the list have a higher precedence than those which come later.

copyup specifies which copy-up mode is used to provide copy-on-write semantics in Unionfs. Possible values are preserve, currentuser, and mounter. Preserve keeps the permissions in the higher-precedence directory the same as in the lower-precedence directory. If currentuser is selected, then the copied-up file will be owned by the user whose actions initiated the copy-up operation. Finally, mounter uses an owner and permission specified at mount time.

copyupuid specifies the uid of the copied-up files.

copyupgidq specifies the gid of the copied-up files.

copyupmode specifies the mode of the copied-up files.

debug specifies the FiST debugging level. 1 through 8 specify individual log-levels. If debug is set to 11 through 18, the output will include debug-10 and all lower levels. If you set this to a non-zero value lots of output will be sent to the kernel ring buffer, some of which may be sensitive.

delete controls how Unionfs deletes and renames objects. Possible values are "all", "first", and "whiteout".

err controls how errors are handled. The default option, "tryleft" causes Unionfs to retry operations in higher priority branches until they suceed. "passup" causes Unionfs to immediately fail and return an error to the user. Using the passup option may violate POSIX file system semantics.

setattr controls how the VFS setattr method will function. Possible values are "all" and "left". Left changes the attributes only on the leftmost (highest priority) branch, whereas "all" changes the attributes on all branches.

AUTHORS
Charles Wright <cwright@cs.sunysb.edu>, Mohammad Zubair <mzubair@ic.sunysb.edu>, Erez Zadok <ezk@cs.sunysb.edu>

SEE ALSO
unionctl(1), uniondbg(1), http://www.fsl.cs.sunysb.edu/