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FreeBSD man pages : chmod (2)
CHMOD(2)		  FreeBSD System Calls Manual		      CHMOD(2)

NAME

chmod, fchmod, lchmod - change mode of file

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/stat.h> int chmod(const char *path, mode_t mode); int fchmod(int fd, mode_t mode); int lchmod(const char *path, mode_t mode);

DESCRIPTION

The file permission bits of the file named specified by path or refer- enced by the file descriptor fd are changed to mode. The chmod() func- tion verifies that the process owner (user) either owns the file speci- fied by path (or fd), or is the super-user. The chmod() function follows symbolic links to operate on the target of the link rather than the link itself. The lchmod function is similar to chmod() but does not follow symbolic links. A mode is created from or'd permission bit masks defined in <sys/stat.h>: #define S_IRWXU 0000700 /* RWX mask for owner */ #define S_IRUSR 0000400 /* R for owner */ #define S_IWUSR 0000200 /* W for owner */ #define S_IXUSR 0000100 /* X for owner */ #define S_IRWXG 0000070 /* RWX mask for group */ #define S_IRGRP 0000040 /* R for group */ #define S_IWGRP 0000020 /* W for group */ #define S_IXGRP 0000010 /* X for group */ #define S_IRWXO 0000007 /* RWX mask for other */ #define S_IROTH 0000004 /* R for other */ #define S_IWOTH 0000002 /* W for other */ #define S_IXOTH 0000001 /* X for other */ #define S_ISUID 0004000 /* set user id on execution */ #define S_ISGID 0002000 /* set group id on execution */ #define S_ISVTX 0001000 /* sticky bit */ #ifndef _POSIX_SOURCE #define S_ISTXT 0001000 #endif The FreeBSD VM system totally ignores the sticky bit (ISVTX) for executa- bles. On UFS-based filesystems (FFS, MFS, LFS) the sticky bit may only be set upon directories. If mode ISVTX (the `sticky bit') is set on a directory, an unprivileged user may not delete or rename files of other users in that directory. The sticky bit may be set by any user on a directory which the user owns or has appropriate permissions. For more details of the properties of the sticky bit, see sticky(8). If mode ISUID (set UID) is set on a directory, and the MNT_SUIDDIR option was used in the mount of the filesystem, then the owner of any new files and sub-directories created within this directory are set to be the same as the owner of that directory. If this function is enabled, new direc- tories will inherit the bit from their parents. Execute bits are removed from the file, and it will not be given to root. This behavior does not change the requirements for the user to be allowed to write the file, but only the eventual owner after it has been created. Group inheritance is not affected. This feature is designed for use on fileservers serving PC users via ftp, SAMBA, or netatalk. It provides security holes for shell users and as such should not be used on shell machines, especially on home directo- ries. This option requires the SUIDDIR option in the kernel to work. Only UFS filesystems support this option. For more details of the suid- dir mount option, see mount(8). 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 sys- tem 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 VALUES

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable 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. [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 translat- ing 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. [EFTYPE] An attempt was made to set the sticky bit upon an exe- cutable. 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), chown(2), open(2), stat(2), sticky(8)

STANDARDS

The chmod() function call is expected to conform to ISO/IEC 9945-1:1990 (``POSIX.1''), except for the return of EFTYPE and the use of S_ISTXT.

HISTORY

A chmod() function call appeared in Version 7 AT&T UNIX. The fchmod() function call appeared in 4.2BSD. The lchmod() function call appeared in FreeBSD 3.0. FreeBSD 4.8 June 4, 1993 FreeBSD 4.8