1999-11-02 21:51:42 +08:00
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[NAME]
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chmod \- change file access permissions
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1998-09-13 04:12:55 +08:00
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[DESCRIPTION]
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This manual page
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documents the GNU version of
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.BR chmod .
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.B chmod
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changes the permissions of each given file according to
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.IR mode ,
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which can be either a symbolic representation of changes to make, or
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an octal number representing the bit pattern for the new permissions.
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.PP
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The format of a symbolic mode is
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`[ugoa...][[+-=][rwxXstugo...]...][,...]'. Multiple symbolic
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operations can be given, separated by commas.
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.PP
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A combination of the letters `ugoa' controls which users' access to
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the file will be changed: the user who owns it (u), other users in the
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file's group (g), other users not in the file's group (o), or all
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users (a). If none of these are given, the effect is as if `a' were
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given, but bits that are set in the umask are not affected.
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.PP
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The operator `+' causes the permissions selected to be added to the
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existing permissions of each file; `-' causes them to be removed; and
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`=' causes them to be the only permissions that the file has.
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.PP
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The letters `rwxXstugo' select the new permissions for the affected
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users: read (r), write (w), execute (or access for directories) (x),
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execute only if the file is a directory or already has execute
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permission for some user (X), set user or group ID on execution (s),
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save program text on swap device (t), the permissions that the user
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who owns the file currently has for it (u), the permissions that other
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users in the file's group have for it (g), and the permissions that
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other users not in the file's group have for it (o).
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.PP
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A numeric mode is from one to four octal digits (0-7), derived by
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adding up the bits with values 4, 2, and 1. Any omitted digits are
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assumed to be leading zeros. The first digit selects the set user ID
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(4) and set group ID (2) and save text image (1) attributes. The
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second digit selects permissions for the user who owns the file: read
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(4), write (2), and execute (1); the third selects permissions for
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other users in the file's group, with the same values; and the fourth
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for other users not in the file's group, with the same values.
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.PP
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.B chmod
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never changes the permissions of symbolic links; the
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.B chmod
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system call cannot change their permissions. This is not a problem
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since the permissions of symbolic links are never used.
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However, for each symbolic link listed on the command line,
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.B chmod
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changes the permissions of the pointed-to file.
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In contrast,
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.B chmod
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ignores symbolic links encountered during recursive directory
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traversals.
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.SH OPTIONS
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