MAN page from Mandriva 2010 coreutils-doc-7.5-2.1mdv2010.0.i586.rpm

CHMOD

Section: User Commands (1)
Updated: August 2009
Index

NAME

chmod - change file mode bits

SYNOPSIS

chmod[OPTION]... MODE[,MODE]... FILE...
chmod[OPTION]... OCTAL-MODE FILE...
chmod[OPTION]... --reference=RFILE FILE...

DESCRIPTION

This manual pagedocuments the GNU version ofchmod.chmodchanges the file mode bits of each given file according tomode,which can be either a symbolic representation of changes to make, oran octal number representing the bit pattern for the new mode bits.

The format of a symbolic mode is [ugoa...][[+-=][perms...]...],wherepermsis either zero or more letters from the setrwxXst, or a single letter from the set ugo.Multiple symbolicmodes can be given, separated by commas.

A combination of the letters ugoa controls which users' accessto the file will be changed: the user who owns it (u), otherusers in the file's group (g), other users not in the file'sgroup (o), or all users (a). If none of these are given,the effect is as if a weregiven, but bits that are set in the umask are not affected.

The operator + causes the selected file mode bits to be added tothe existing file mode bits of each file; - causes them to beremoved; and = causes them to be added and causes unmentionedbits to be removed except that a directory's unmentioned set user andgroup ID bits are not affected.

The letters rwxXst select file mode bits for the affected users:read (r), write (w), execute (or search for directories)(x), execute/search only if the file is a directory or alreadyhas execute permission for some user (X), set user or group IDon execution (s), restricted deletion flag or sticky bit(t). Instead of one or more of these letters, you can specifyexactly one of the letters ugo: the permissions granted to theuser who owns the file (u), the permissions granted to otherusers who are members of the file's group (g),and the permissions granted to users that are in neither of the two precedingcategories (o).

A numeric mode is from one to four octal digits (0-7), derived byadding up the bits with values 4, 2, and 1. Omitted digits areassumed to be leading zeros.The first digit selects the set user ID (4) and set group ID (2) andrestricted deletion or sticky (1) attributes. The second digitselects permissions for the user who owns the file: read (4), write (2),and execute (1); the third selects permissions for other users in thefile's group, with the same values; and the fourth for other users notin the file's group, with the same values.

chmodnever changes the permissions of symbolic links; thechmodsystem call cannot change their permissions. This is not a problemsince the permissions of symbolic links are never used.However, for each symbolic link listed on the command line,chmodchanges the permissions of the pointed-to file.In contrast,chmodignores symbolic links encountered during recursive directorytraversals.

SETUID AND SETGID BITS

chmodclears the set-group-ID bit of aregular file if the file's group ID does not match the user'seffective group ID or one of the user's supplementary group IDs,unless the user has appropriate privileges. Additional restrictionsmay cause the set-user-ID and set-group-ID bits ofMODEorRFILEto be ignored. This behavior depends on the policy andfunctionality of the underlyingchmodsystem call. When indoubt, check the underlying system behavior.

chmodpreserves a directory's set-user-ID and set-group-ID bits unless youexplicitly specify otherwise. You can set or clear the bits withsymbolic modes likeu+sandg-s,and you can set (but not clear) the bits with a numeric mode.

RESTRICTED DELETION FLAG OR STICKY BIT

The restricted deletion flag or sticky bit is a single bit, whoseinterpretation depends on the file type. For directories, it preventsunprivileged users from removing or renaming a file in the directoryunless they own the file or the directory; this is called therestricted deletion flagfor the directory, and is commonly found on world-writable directorieslike /tmp. For regular files on some older systems, the bitsaves the program's text image on the swap device so it will load morequickly when run; this is called thesticky bit.

OPTIONS

Change the mode of each FILE to MODE.

-c, --changes: like verbose but report only when a change is made
--no-preserve-root: do not treat `/' specially (the default)
--preserve-root: fail to operate recursively on `/'
-f, --silent, --quiet: suppress most error messages
-v, --verbose: output a diagnostic for every file processed
--reference=RFILE: use RFILE's mode instead of MODE values
-R, --recursive: change files and directories recursively
--help: display this help and exit
--version: output version information and exit

Each MODE is of the form `[ugoa]*([-+=]([rwxXst]*|[ugo]))+'.

AUTHOR

Written by David MacKenzie and Jim Meyering.

REPORTING BUGS

Report chmod bugs to bug-coreutilsAATTgnu.org
GNU coreutils home page: <http://www.gnu.org/software/coreutils/>
General help using GNU software: <http://www.gnu.org/gethelp/>

COPYRIGHT

Copyright © 2009 Free Software Foundation, Inc.License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.There is NO WARRANTY, to the extent permitted by law.

Index

NAME
SYNOPSIS
DESCRIPTION
SETUID AND SETGID BITS
RESTRICTED DELETION FLAG OR STICKY BIT
OPTIONS
AUTHOR
REPORTING BUGS
COPYRIGHT
SEE ALSO

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