System Calls chmod(2)
NAME
chmod, fchmod, fchmodat - change access permission mode of
fileSYNOPSIS
#include
int chmod(const char *path, mode_t mode);
int fchmod(int fildes, mode_t mode);
int fchmodat(int fd, const char *path, mode_t mode, int flag);
DESCRIPTION
The chmod() and fchmod() functions set the access permission portion of the mode of the file whose name is given by path or referenced by the open file descriptor fildes to the bitpattern contained in mode. Access permission bits are inter-
preted as follows:S_ISUID 04000 Set user ID on execution.
S_ISGID 020#0 Set group ID on execution if # is 7, 5,
3, or 1. Enable mandatory file/recordlocking if # is 6, 4, 2, or 0.
S_ISVTX 01000 Sticky bit.
S_IRWXU 00700 Read, write, execute by owner.
S_IRUSR 00400 Read by owner.
S_IWUSR 00200 Write by owner.
S_IXUSR 00100 Execute (search if a directory) by
owner.S_IRWXG 00070 Read, write, execute by group.
S_IRGRP 00040 Read by group.
S_IWGRP 00020 Write by group.
S_IXGRP 00010 Execute by group.
S_IRWXO 00007 Read, write, execute (search) by others.
S_IROTH 00004 Read by others.
S_IWOTH 00002 Write by others.
S_IXOTH 00001 Execute by others.
Modes are constructed by the bitwise OR operation of the access permission bits. The effective user ID of the process must match the owner of the file or the process must have the appropriate privilegeSunOS 5.11 Last change: 6 Jul 2010 1
System Calls chmod(2) to change the mode of a file. If the process is not a privileged process and the file isnot a directory, mode bit 01000 (save text image on execu-
tion) is cleared. If neither the process is privileged nor the file's group is a member of the process's supplementary group list, and the effective group ID of the process does not match the group ID of the file, mode bit 02000 (set group ID on execution) is cleared.If a directory is writable and has S_ISVTX (the sticky bit)
set, files within that directory can be removed or renamed only if one or more of the following is true (see unlink(2) and rename(2)): o the user owns the file o the user owns the directory o the file is writable by the user o the user is a privileged userIf a regular file is not executable and has S_ISVTX set, the
file is assumed to be a swap file. In this case, the system's page cache will not be used to hold the file'sdata. If the S_ISVTX bit is set on any other file, the
results are unspecified. If a directory has the set group ID bit set, a given file created within that directory will have the same group ID as the directory. Otherwise, the newly created file's group ID will be set to the effective group ID of the creating process. If the mode bit 02000 (set group ID on execution) is set and the mode bit 00010 (execute or search by group) is not set, mandatory file/record locking will exist on a regular file, possibly affecting future calls to open(2), creat(2), read(2), and write(2) on this file. If fildes references a shared memory object, fchmod() needonly affect the S_IRUSR, S_IRGRP, S_IROTH, S_IWUSR, S_IWGRP,
SunOS 5.11 Last change: 6 Jul 2010 2
System Calls chmod(2)S_IWOTH, S_IXUSR, S_IXGRP, and S_IXOTH file permission bits.
If fildes refers to a socket, fchmod() does not fail but no action is taken. If fildes refers to a stream that is attached to an object in the file system name space with fattach(3C), the fchmod() call performs no action and returns successfully. Upon successful completion, chmod() and fchmod() mark forupdate the st_ctime field of the file.
The fchmodat() function is equivalent to chmod() except in
the case where path specifies a relative path. In this casethe file to be changed is determined relative to the direc-
tory associated with the file descriptor fd instead of the current working directory. If the file descriptor was openedwithout O_SEARCH, the function checks whether directory
searches are permitted using the current permissions of the directory underlying the file descriptor. If the filedescriptor was opened with O_SEARCH, the function does not-
perform the check.Values for flag are constructed by a bitwise-inclusive OR of
flags from the following list, defined inAT_SYMLINK_NOFOLLOW If path names a symbolic link, then
the mode of the symbolic link is changed.If fchmodat() is passed the special value AT_FDCWD in the fd
parameter, the current working directory is used. If flag is also 0, the behavior shall be identical to a call to chmod().RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, -1 is
returned, the file mode is unchanged, and errno is set to indicate the error.ERRORS
The chmod(), fchmod(), and fchmodat() functions will fail
if:SunOS 5.11 Last change: 6 Jul 2010 3
System Calls chmod(2) EPERM The effective user ID does not match the owner of the file and the process does not have appropriate privilege.The {PRIV_FILE_OWNER} privilege overrides con-
straints on ownership when changing permissions on a file.The {PRIV_FILE_SETID} privilege overrides con-
straints on ownership when adding the setuid or setgid bits to an executable file or a directory.When adding the setuid bit to a root owned execut-
able, additional restrictions apply. See privileges(5).EROFS The file referred to by path resides on a read-only
file system. The chmod() and fchmod() functions will fail if:EIO An I/O error occurred while reading from or writing to the file system.
The chmod() and fchmodat()functions will fail if:
EACCES Search permission is denied on a component of the path prefix of path. The privilege{FILE_DAC_SEARCH} overrides file permissions
restrictions in that case. ELOOP A loop exists in symbolic links encountered during the resolution of the path argument.ENAMETOOLONG The length of the path argument exceeds
PATH_MAX, or the length of a path component
exceeds NAME_MAX while _POSIX_NO_TRUNC is in
effect. ENOENT Either a component of the path prefix or the file referred to by path does not exist or is a null pathname.SunOS 5.11 Last change: 6 Jul 2010 4
System Calls chmod(2) ENOTDIR A component of the prefix of path is not a directory. The chmod() function will fail if: EFAULT The path argument points to an illegal address. ENOLINK The fildes argument points to a remote machine and the link to that machine is no longer active. The fchmod() function will fail if:EBADF The fildes argument is not an open file descrip-
tor ENOLINK The path argument points to a remote machine and the link to that machine is no longer active.The fchmodat() function will fail if:
EACCES fd was not opened with O_SEARCH and the permis-
sions of the directory underlying fd do not permit directory searches. EBADF The path argument does not specify an absolutepath and the fd argument is neither AT_FDCWD nor a
valid file descriptor open for reading or search-
ing.The chmod(), fchmod(), and fchmodat() functions may fail if:
EINTR A signal was caught during execution of the func-
tion. EINVAL The value of the mode argument is invalid.The chmod() and fchmodat() functions may fail if:
SunOS 5.11 Last change: 6 Jul 2010 5
System Calls chmod(2)ELOOP More than {SYMLOOP_MAX} symbolic links were
encountered during the resolution of the path argument.ENAMETOOLONG As a result of encountering a symbolic link
in resolution of thepath argument, the length of the substituted pathname stringsexceeds {PATH_MAX}.
The fchmod() function may fail if:EINVAL The fildes argument refers to a pipe and the sys-
tem disallows execution of this function on a pipe.The fchmodat() function may fail if:
EINVAL The value of the flag argument is invalid ENOTDIR The path argument is not an absolute path andfd is neither AT_FDCWD nor a file descriptor
associated with a directoryEOPNOTSUPP The AT_SYMLINK_NOFOLLOW bit is set in the flag
argument, path names a symbolic link, and the system does not support changing the mode of a symbolic link.EXAMPLES
Example 1 Set Read Permissions for User, Group, and Others The following example sets read permissions for the owner, group, and others.#include
const char *path; ...chmod(path, S_IRUSR|S_IRGRP|S_IROTH);
Example 2 Set Read, Write, and Execute Permissions for the Owner OnlySunOS 5.11 Last change: 6 Jul 2010 6
System Calls chmod(2)The following example sets read, write, and execute permis-
sions for the owner, and no permissions for group and oth-
ers.#include
const char *path; ...chmod(path, S_IRWXU);
Example 3 Set Different Permissions for Owner, Group, and Other The following example sets owner permissions for CHANGEFILE to read, write, and execute, group permissions to read and execute, and other permissions to read.#include
#define CHANGEFILE "/etc/myfile"
...chmod(CHANGEFILE, S_IRWXU|S_IRGRP|S_IXGRP|S_IROTH);
Example 4 Set and Checking File Permissions The following example sets the file permission bits for a file named /home/cnd/mod1, then calls the stat(2) function to verify the permissions.#include
int status; struct stat buffer ...chmod("home/cnd/mod1", S_IRWXU|S_IRWXG|S_IROTH|S_IWOTH);
status = stat("home/cnd/mod1", &buffer;);USAGE
If chmod() or fchmod() is used to change the file groupowner permissions on a file with non-trivial ACL entries,
only the ACL mask is set to the new permissions and the group owner permission bits in the file's mode field(defined in mknod(2)) are unchanged. A non-trivial ACL
entry is one whose meaning cannot be represented in the file's mode field alone. The new ACL mask permissions might change the effective permissions for additional users and groups that have ACL entries on the file.SunOS 5.11 Last change: 6 Jul 2010 7
System Calls chmod(2)ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | Async-Signal-Safe |
|_____________________________|_____________________________|
| Standard | See standards(5). ||_____________________________|_____________________________|
SEE ALSO
chmod(1), chown(2), creat(2), fcntl(2), mknod(2), open(2), read(2), rename(2), stat(2), write(2), fattach(3C), mkfifo(3C), stat.h(3HEAD), attributes(5), privileges(5), standards(5) Programming Interfaces GuideSunOS 5.11 Last change: 6 Jul 2010 8