CHMOD(1)

📦
version 9.10 · 5 versions
, in ubuntu stonking

💖 CHMOD(1) 💖

okay so bestie, gather round 🫶 because this is the User Commands manual page for chmod — yes, that's the manual name, folded in right here like a little bow 🎀 — and specifically it's the GNU version's page, so don't come at me with some other implementation's lore. This is the page that teaches you how to change file mode bits, and honestly? iconic. lowkey the most-used command in your whole terminal. let's get into it 💅

🌸 NAME 🌸

chmod — change file mode bits ✨

🦋 SYNOPSIS 🦋

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

so there's three whole vibes here, and you pick one:

  • hand it one or more MODEs (commas between them, plural, we love that), then one or more FILEs
  • hand it a single OCTAL-MODE and then your FILEs
  • hand it --reference=RFILE and let some other file be the blueprint 🌈

🌸 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 representing 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. yes, you can stack them. no, you don't have to. 💅

who's getting affected tho? 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. sneaky little caveat, no cap.

the operators, the moment. 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. read that last clause twice, it's giving "exception to the exception" 🫠

the letters. 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). copy permissions from another class, we love a shortcut 🦋

numbers, for the math girlies. 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. 4 = read, 2 = write, 1 = execute, add them up, periodt.

symlink drama, because of course. chmod doesn't change the permissions of symbolic links; the chmod system call cannot change their permissions on most systems, and most systems ignore permissions of symbolic links. 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. Options that modify this behavior are described in the OPTIONS section. 💀

👑 SETUID AND SETGID BITS 👑

chmod clears the set-group-ID bit of a regular file if the file's group ID does not match the user's effective group ID or one of the user's supplementary group IDs, unless the user has appropriate privileges. Additional restrictions may cause the set-user-ID and set-group-ID bits of MODE or RFILE to be ignored. This behavior depends on the policy and functionality of the underlying chmod system call. When in doubt, check the underlying system behavior. fr fr, it's not our call.

For directories chmod preserves set-user-ID and set-group-ID bits unless you explicitly specify otherwise. You can set or clear the bits with symbolic modes like u+s and g-s. To clear these bits for directories with a numeric mode requires an additional leading zero like 00755, leading minus like -6000, or leading equals like =755. note the leading zero, bestie, that's the whole trick ✨

🍓 RESTRICTED DELETION FLAG OR STICKY BIT 🍓

The restricted deletion flag or sticky bit is a single bit, whose interpretation depends on the file type. For directories, it prevents unprivileged users from removing or renaming a file in the directory unless they own the file or the directory; this is called the restricted deletion flag for the directory, and is commonly found on world-writable directories like /tmp. For regular files on some older systems, the bit saves the program's text image on the swap device so it will load more quickly when run; this is called the sticky bit. same bit, two completely different eras of lore 🧚

✨ OPTIONS ✨

Change the mode of each FILE to MODE. With --reference, change the mode of each FILE to that of RFILE.

  • -c, --changes — like verbose but report only when a change is made
  • -f, --silent, --quiet — suppress most error messages
  • -v, --verbose — output a diagnostic for every file processed
  • --dereference — affect the referent of each symbolic link, rather than the symbolic link itself
  • -h, --no-dereference — affect each symbolic link, rather than the referent
  • --no-preserve-root — do not treat / specially (the default)
  • --preserve-root — fail to operate recursively on /
  • --reference=RFILE — use RFILE's mode instead of specifying MODE values. RFILE is always dereferenced if a symbolic link.
  • -R, --recursive — change files and directories recursively

🌈 how the traversal goes down (only matters with -R) 🌈

The following options modify how a hierarchy is traversed when the -R option is also specified. If more than one is specified, only the final one takes effect. -H is the default.

  • -H — if a command line argument is a symlink to a directory, traverse it
  • -L — traverse every symbolic link to a directory encountered
  • -P — do not traverse any symbolic links
bestie, "only the final one takes effect" is a real warning, not a cute flourish. stack them all you want, last one wins. 🫶
  • --help — display this help and exit
  • --version — output version information and exit

Each MODE is of the form '[ugoa]*([-+=]([rwxXst]*|[ugo]))+|[-+=][0-7]+'. yes. that's the whole grammar. look at it. she's beautiful. 💖

💜 AUTHOR 💜

Written by David MacKenzie and Jim Meyering. legends, honestly.

🐛 REPORTING BUGS 🐛

🔥 SEE ALSO 🔥

Packaged by Ubuntu (9.10-1ubuntu2) Copyright © 2026 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later https://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.

and that's the page, bestie 🎀 GNU coreutils 9.10, August 2026 — that's the source, the version, and the date, all wrapped up in a bow. go forth and chmod responsibly, and remember: with great permission bits comes great responsibility. slay 💅✨

📦 where this page comes from