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4.2 File System Types

4.2.2 Translucent File System (TFS)

The translucent file system allows users to mount a writable file system on top of a read-only file system. The contents of the lower system remain visible when the file system is mounted in this way, so long as there is no file system of similar name in the top file system (SunOS 4.1.X only).

So TFS is a series of stacked file systems where searching for files is done from the top of the stack downward until the first file of that name is found.

Modification of files can be done on the top most file system only. If a user tries to remove a file from a directory not in the foremost file system TFS creates a whiteout in the topmost file system and leaves the lower one intact. Further attempts by the user to access that file are answered as if the file had been removed, when in fact it is still intact at the lower file system, and can be accessed by other users not using TFS.

TFS requires both the LOFS (loopback filesystem) and TFS (translucent filesystem) options be compiled into the kernel. It also requires the following line in the /etc/inetd.conf file:

tfsd/1-2 dgram rpc/udp wait root /usr/etc/tfsd tfsd

To mount a TFS file system use the following command:

# mount -t tfs /src/fgf/test /usr/bin

Unmount with:

# umount /usr/bin

Unix System Administration - 8 AUG 1996
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