chmod.2 (2010 09)

c
chmod(2) chmod(2)
NAME
chmod(), fchmod() - change file mode access permissions
SYNOPSIS
#include <sys/stat.h>
int chmod(const char *path, mode_t mode);
int fchmod(int fildes, mode_t mode);
DESCRIPTION
The chmod() and fchmod() system calls set the access permission portion of the file’s mode according
to the bit pattern contained in mode. path points to a path name naming a file. fildes is a file descriptor.
The following symbolic constants representing the access permission bits are defined with the indicated
values in
<sys/stat.h> and are used to construct the mode argument. The value of mode is the bit-
wise inclusive OR of the values for the desired permissions.
S_ISUID 04000 Set user ID on execution.
S_ISGID 02000 Set group ID on execution.
S_ENFMT 02000 Record locking enforced.
S_ISVTX 01000 Sticky bit (see below).
S_IRUSR 00400 Read by owner.
S_IWUSR 00200 Write by owner.
S_IXUSR 00100 Execute (search) by owner.
S_IRGRP 00040 Read by group.
S_IWGRP 00020 Write by group.
S_IXGRP 00010 Execute (search) by group.
S_IROTH 00004 Read by others (that is, anybody else).
S_IWOTH 00002 Write by others.
S_IXOTH 00001 Execute (search) by others.
The mode bit
S_ENFMT (same as S_ISGID) is used to enforce file-locking mode (see lockf (2), fcntl (2),
and flock(2)) on files that are not group executable. This might affect future calls to
open(), creat(),
read(), write(), truncate(), and ftruncate() on such files (see open (2), creat (2), read (2),
write (2), and truncate (2)).
The mode bit
S_ISVTX (sticky bit) has no significance when set on a regular file.
If the path given to
chmod() contains a symbolic link as the last element, this link is traversed and path
name resolution continues. chmod() changes the access mode of the symbolic link’s target, rather than
the access mode of the link.
Access Control Lists - HFS File Systems Only
All optional entries in a file’s access control list are deleted when
chmod() is executed. (This behavior
conforms to the IEEE Standard POSIX 1003.1-1988.) To preserve optional entries in a file’s access control
list, it is necessary to save and restore them using
getacl() and setacl() (see getacl (2) and
setacl (2)).
To set the permission bits of access control list entries, use
setacl() instead of chmod().
Access Control Lists - JFS File Systems Only
The effective permissions granted by optional entries in a file’s access control list may be changed when
chmod() is executed. In particular, using chmod() to remove read, write and execute permissions
from a file’s owner, owning group, and all others works as expected, because chmod() affects the
class entry in the ACL, limiting any access that can be granted to additional users or groups via
optional ACL entries. The effect can be verified by doing a getacl on the file after the chmod(), and
noting that all optional (non-default) ACL entries with nonzero permissions also have the comment #
effective:---.
To set the permission bits of access control list entries, use
setacl() instead of chmod().
For more information on access control list entries, see acl (5) and aclv (5).
Security Restrictions
To change the mode of a file, the effective user ID of the process must match that of the owner of the file
or the process must have the
OWNER privilege.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1