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Top Forums UNIX for Dummies Questions & Answers About read,write & execute permissons of a directory Post 302281990 by pludi on Friday 30th of January 2009 01:52:14 AM
Old 01-30-2009
The first number in this group of 4 is for the special bits. '0' means nothing, '1' is the "sticky bit", '2' the "set group ID", and '4' the "set user ID" bit. '4' is probably the most used of those, as it changes execution of a program so that it doesn't run as the calling UID, but as the one of the file owner (same for the SGID bit, only with the group instead of the user). The passwd utility most often has this one set, as it requires root privileges to change the password file, but any user should be able to run it.

The effects of the "sticky bit" vary between platforms, and whether it's set on a file or directory. For files it originally was intended to tell the kernel "Keep this file in memory after it ended" so that subsequent calls wouldn't need to reread it from disk (not working in Linux). For directories it means "only the owner of this file may manipulate it", eg. on the /tmp dir, where every user may write, but others shouldn't be able to delete or modify a file there.

The first character in an ls -l output (in your example 'd') specifies the file type. '-' is a regular file, 'd' is a directory, 'c' is a character device, ....

HTH
 

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sticky(5)						Standards, Environments, and Macros						 sticky(5)

NAME
sticky - mark files for special treatment DESCRIPTION
The sticky bit (file mode bit 01000, see chmod(2)) is used to indicate special treatment of certain files and directories. A directory for which the sticky bit is set restricts deletion of files it contains. A file in a sticky directory can only be removed or renamed by a user who has write permission on the directory, and either owns the file, owns the directory, has write permission on the file, or is a privi- leged user. Setting the sticky bit is useful for directories such as /tmp, which must be publicly writable but should deny users permission to arbitrarily delete or rename the files of others. If the sticky bit is set on a regular file and no execute bits are set, the system's page cache will not be used to hold the file's data. This bit is normally set on swap files of diskless clients so that accesses to these files do not flush more valuable data from the sys- tem's cache. Moreover, by default such files are treated as swap files, whose inode modification times may not necessarily be correctly recorded on permanent storage. Any user may create a sticky directory. See chmod for details about modifying file modes. SEE ALSO
chmod(1), chmod(2), chown(2), mkdir(2), rename(2), unlink(2) BUGS
The mkdir(2) function will not create a directory with the sticky bit set. SunOS 5.11 1 Aug 2002 sticky(5)
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