chmod - Change File Mode Bits

CHMOD(1) User Commands CHMOD(1) 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 page documents the GNU version of chmod. chmod changes the file mode bits of each given file according to mode, which can be either a symbolic representation of changes to make, or an octal number repre‐ senting the bit pattern for the new mode bits. The format of a symbolic mode is [ugoa...][[‐+=][perms...]...], where perms is either zero or more letters from the set rwxXst, or a single letter from the set ugo. Multiple symbolic modes can be given, separated by commas. A combination of the letters ugoa controls which users’ access to the file will be changed: the user who owns it (u), other users in the file’s group (g), other users not in the file’s group (o), or all users (a). If none of these are given, the effect is as if (a) were given, but bits that are set in the umask are not affected. The operator + causes the selected file mode bits to be added to the existing file mode bits of each file; ‐ causes them to be removed; and = causes them to be added and causes unmentioned bits to be removed except that a directory’s unmentioned set user and group 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 already has execute permission for some user (X), set user or group ID on execution (s), restricted deletion flag or sticky bit (t). Instead of one or more of these letters, you can specify exactly one of the letters ugo: the permissions granted to the user who owns the file (u), the permissions granted to other users who are members of the file’s group (g), and the permissions granted to users that are in neither of the two preceding categories (o). A numeric mode is from one to four octal digits (0-7), derived by adding up the bits with values 4, 2, and 1. Omitted digits are assumed to be leading zeros. The first digit selects the set user ID (4) and set group ID (2) and restricted deletion or sticky (1) attributes. The second digit selects permissions for the user who owns the file: read (4), write (2), and execute (1); the third selects permissions for other users in the file’s group, with the same values; and the fourth for other users not in the file’s group, with the same values. chmod never changes the permissions of symbolic links; the chmod system call cannot change their permissions. This is not a problem since the permissions of symbolic links are never used. However, for each symbolic link listed on the command line, chmod changes the permissions of the pointed‐to file. In contrast, chmod ignores symbolic links encountered during recursive directory traversals.

This manual page describes the GNU version of the chmod command, which is used to change the file mode bits of files. The mode can be specified either as a symbolic representation of changes or as an octal number. The symbolic mode uses letters like 'ugoa' to specify users and operators like '+-=' to add, remove, or set permissions. The octal mode uses digits to represent the bit pattern for the new mode bits. Chmod changes the permissions of the pointed-to file instead of the symbolic link itself, and ignores symbolic links during recursive directory traversals.