--- name: "chmod" section: "1" platform: "openbsd" package: "man" version: "8.0-current-20261101" release: "OpenBSD 8.0-current (2026-11-01)" platforms: ["linux", "freebsd", "openbsd", "macos"] url: "https://new.carta.tech/chmod" --- # chmod(1) change file modes ## NAME **chmod** – change file modes ## SYNOPSIS **chmod** \[**-h**\]\[ **-R** \[**-H** \| **-L** \| **-P**\]\] *mode* *file ...* ## DESCRIPTION The **chmod** utility modifies the file mode bits of the listed files as specified by the *mode* operand. The mode of a file dictates its permissions, among other attributes. The options are as follows: - **-H** If the **-R** option is also specified, symbolic links on the command line are followed. Symbolic links encountered in the tree traversal are not followed. - **-h** Treat symbolic links like other files: modify links instead of following them. The **-h** and **-R** options are mutually exclusive. - **-L** If the **-R** option is also specified, all symbolic links are followed. - **-P** If the **-R** option is also specified, no symbolic links are followed. - **-R** Recurse. Where *file* is a directory, change the mode of the directory and all the files and directories in the file hierarchy below it. Symbolic links have modes, but those modes have no effect on the kernel's access checks. The **-H**, **-L**, and **-P** options are ignored unless the **-R** option is specified; if none of them are given, the default is to not follow symbolic links. In addition, these options override each other and the command's actions are determined by the last one specified. Only the file's owner or the superuser is permitted to change the mode of a file. ### Absolute modes Absolute modes are specified according to the following format: **chmod** *nnnn* *file ...* An absolute mode is an octal number (specified as *nnnn*, where *n* is a number from 0 to 7) constructed by ORing any of the following values: - 0400 Allow read by owner. - 0200 Allow write by owner. - 0100 Allow execution (or search in directories) by owner. - 0700 Allow read, write, and execute/search by owner. - 0040 Allow read by group. - 0020 Allow write by group. - 0010 Allow execution (or search in directories) by group. - 0070 Allow read, write, and execute/search by group. - 0004 Allow read by others. - 0002 Allow write by others. - 0001 Allow execution (or search in directories) by others. - 0007 Allow read, write, and execute/search by others. In addition to the file permission modes, the following mode bits are available: - 4000 Set-user-ID on execution. - 2000 Set-group-ID on execution. - 1000 Enable sticky bit; see [sticky(8)](/sticky/8.md) and [chmod(2)](/chmod/2.md). The execute bit for a directory is often referred to as the “search” bit. In order to access a file, a user must have execute permission in each directory leading up to it in the filesystem hierarchy. For example, to access the file */bin/ls*, execute permission is needed on */*, */bin*, and, of course, the *ls* binary itself. ### Symbolic modes Symbolic modes are specified according to the following format: **chmod** \[*who*\] *op* \[*perm*\],*...* *file ...* The *who* symbols indicate whose permissions are to be changed or assigned: - u User (owner) permissions. - g Group permissions. - o Others permissions. - a All of the above. Do not confuse the ‘o’ symbol with “owner”. It is the user bit, ‘u’, that refers to the owner of the file. The *op* symbols represent the operation performed, as follows: - \+ If no value is supplied for *perm*, the ‘+’ operation has no effect. If no value is supplied for *who*, each permission bit specified in *perm*, for which the corresponding bit in the file mode creation mask is clear, is set. Otherwise, the mode bits represented by the specified *who* and *perm* values are set. - \- If no value is supplied for *perm*, the ‘-’ operation has no effect. If no value is supplied for *who*, each permission bit specified in *perm*, for which the corresponding bit in the file mode creation mask is clear, is cleared. Otherwise, the mode bits represented by the specified *who* and *perm* values are cleared. - \= The mode bits specified by the *who* value are cleared or, if no *who* value is specified, the user, group and other mode bits are cleared. Then, if no value is supplied for *who*, each permission bit specified in *perm*, for which the corresponding bit in the file mode creation mask is clear, is set. Otherwise, the mode bits represented by the specified *who* and *perm* values are set. The *perm* (permission symbols) represent the portions of the mode bits as follows: - r Read bits. - s Set-user-ID and set-group-ID on execution bits. - t Sticky bit. - w Write bits. - x Execute/search bits. - X The execute/search bits if the file is a directory or any of the execute/search bits are set in the original (unmodified) mode. - u User permission bits in the mode of the original file. - g Group permission bits in the mode of the original file. - o Other permission bits in the mode of the original file. Each clause (given in a comma-delimited list on the command line) specifies one or more operations to be performed on the mode bits, and each operation is applied in the order specified. Operations upon the “other” permissions (specified by the symbol ‘o’ by itself), in combination with the *perm* symbols ‘s’ or ‘t’, are ignored. ## EXIT STATUS The **chmod** utility exits 0 on success, and \>0 if an error occurs. ## EXAMPLES Set file readable by anyone and writable by the owner only: ``` $ chmod 644 file ``` Deny write permission to group and others: ``` $ chmod go-w file ``` Set the read and write permissions to the usual defaults, but retain any execute permissions that are currently set: ``` $ chmod =rwX file ``` Make a directory or file searchable/executable by everyone if it is already searchable/executable by anyone: ``` $ chmod +X file ``` Any of these commands will make a file readable/executable by everyone and writable by the owner only: ``` $ chmod 755 file $ chmod u=rwx,go=rx file $ chmod u=rwx,go=u-w file ``` Clear all mode bits for group and others: ``` $ chmod go= file ``` Set the group bits equal to the user bits, but clear the group write bit: ``` $ chmod g=u-w file ``` ## SEE ALSO [chflags(1)](/chflags/1.md), [chgrp(1)](/chgrp/1.md), [find(1)](/find/1.md), [install(1)](/install/1.md), [chmod(2)](/chmod/2.md), [stat(2)](/stat/2.md), [umask(2)](/umask/2.md), [fts\_open(3)](/fts_open/3.md), [setmode(3)](/setmode/3.md), [symlink(7)](/symlink/7.md), [chown(8)](/chown/8.md), [sticky(8)](/sticky/8.md) ## STANDARDS The **chmod** utility is compliant with the IEEE Std 1003.1-2024 (“POSIX.1”) specification. The flags \[**-HhLP**\] are extensions to that specification. The ‘t’ perm symbol (sticky bit) is marked by IEEE Std 1003.1-2024 (“POSIX.1”) as being an X/Open System Interfaces option. ## HISTORY A **chmod** command appeared in Version 1 AT&T UNIX. ## BUGS There's no *perm* option for the naughty bits.