CHMOD

Section: System Calls (2)
Updated: May 13, 1986
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NAME

chmod, fchmod - change mode of file  

SYNOPSIS

chmod(path, mode)
char *path;
int mode;

fchmod(fd, mode)
int fd, mode;
 

DESCRIPTION

The file whose name is given by path or referenced by the descriptor fd has its mode changed to mode. Modes are constructed by or'ing together some combination of the following, defined in <sys/stat.h>: 

S_ISUID   04000   set user ID on execution
S_ISGID   02000   set group ID on execution
S_ISVTX   01000   `sticky bit' (see below)
S_IREAD   00400   read by owner
S_IWRITE  00200   write by owner
S_IEXEC   00100   execute (search on directory) by owner
          00070   read, write, execute (search) by group
          00007   read, write, execute (search) by others

If an executable file is set up for sharing (this is the default) then mode S_ISVTX (the `sticky bit') prevents the system from abandoning the swap-space image of the program-text portion of the file when its last user terminates. Ability to set this bit on executable files is restricted to the super-user.

If mode S_ISVTX (the `sticky bit') is set on a directory, an unprivileged user may not delete or rename files of other users in that directory. For more details of the properties of the sticky bit, see sticky(8).

Only the owner of a file (or the super-user) may change the mode.

Writing or changing the owner of a file turns off the set-user-id and set-group-id bits unless the user is the super-user. This makes the system somewhat more secure by protecting set-user-id (set-group-id) files from remaining set-user-id (set-group-id) if they are modified, at the expense of a degree of compatibility.  

RETURN VALUE

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.  

ERRORS

Chmod will fail and the file mode will be unchanged if:
[ENOTDIR]
A component of the path prefix is not a directory.
[EINVAL]
The pathname contains a character with the high-order bit set.
[ENAMETOOLONG]
A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
[ENOENT]
The named file does not exist.
[EACCES]
Search permission is denied for a component of the path prefix.
[ELOOP]
Too many symbolic links were encountered in translating the pathname.
[EPERM]
The effective user ID does not match the owner of the file and the effective user ID is not the super-user.
[EROFS]
The named file resides on a read-only file system.
[EFAULT]
Path points outside the process's allocated address space.
[EIO]
An I/O error occurred while reading from or writing to the file system.

Fchmod will fail if:

[EBADF]
The descriptor is not valid.
[EINVAL]
Fd refers to a socket, not to a file.
[EROFS]
The file resides on a read-only file system.
[EIO]
An I/O error occurred while reading from or writing to the file system.
 

SEE ALSO

chmod(1), open(2), chown(2), stat(2), sticky(8)

 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
SEE ALSO
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Time: 04:51:40 GMT, January 31, 2023