HP-UX Reference (11i v1 05/09) - 2 System Calls (vol 5)

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 Save text image after execution.
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.
To change the mode of a file, the effective user ID of the process must match that of the owner of the file or
a user with appropriate privileges.
If the effective user ID of the process is not that of a user with appropriate privileges, mode bit
S_ISVTX
is cleared.
If the effective user ID of the process is not that of a user with appropriate privileges, and the effective
group ID of the process does not match the group ID of the file and none of the group IDs in the supple-
mentary groups list match the group ID of the file, mode bit S_ISGID is cleared.
The mode bit
S_ENFMT (same as S_ISGID) is used to enforce file-locking mode (see lockf(2) and fcntl(2))
on files that are not group executable. This might affect future calls to
open(), creat(), read(), and
write() on such files (see open(2), creat(2), read(2), and write(2)).
If an executable file is prepared for sharing, mode bit
S_ISVTX prevents the system from abandoning the
swap-space image of the program-text portion of the file when its last user terminates. Then, when the
next user of the file executes it, the text need not be read from the file system but can simply be swapped
in, thus saving time.
If the mode bit S_ISVTX (sticky bit) is set on a directory, files inside the directory may be renamed or
removed only by the owner of the file, the owner of the directory, or the superuser (even if the modes of the
directory would otherwise allow such an operation).
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().
HP-UX 11i Version 1: September 2005 − 1 − Hewlett-Packard Company Section 2−−33