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Technical Reference: Base Operating System and Extensions, Volume 1
Changes file access
permissions.
Standard C Library
(libc.a)
#include <sys/stat.h>
int chmod ( Path, Mode)
const char *Path;
mode_t Mode;
int fchmod ( FileDescriptor, Mode)
int FileDescriptor;
mode_t Mode;
The chmod subroutine
sets the access permissions of the file specified by the Path
parameter. If Network File System (NFS) is installed on your system,
this path can cross into another node.
Use the fchmod
subroutine to set the access permissions of an open file pointed to by the
FileDescriptor parameter.
The access control information is
set according to the Mode parameter.
| FileDescriptor
| Specifies the file descriptor of an open file.
|
| Mode
| Specifies the bit pattern that determines the access permissions.
The Mode parameter is constructed by logically ORing one or more of
the following values, which are defined in the sys/mode.h file:
- S_ISUID
- Enables the setuid attribute for an executable file. A
process executing this program acquires the access rights of the owner of the
file.
- S_ISGID
- Enables the setgid attribute for an executable file. A
process executing this program acquires the access rights of the group of the
file. Also, enables the group-inheritance attribute for a
directory. Files created in this directory have a group equal to the
group of the directory.
The following attributes apply only to
files that are directly executable. They have no meaning when applied
to executable text files such as shell scripts and awk
scripts.
- S_ISVTX
- Enables the link/unlink attribute for a directory. Files
cannot be linked to in this directory. Files can only be unlinked if
the requesting process has write permission for the directory and is either
the owner of the file or the directory.
- S_ISVTX
- Enables the save text attribute for an executable file.
The program is not unmapped after usage.
- S_ENFMT
- Enables enforcement-mode record locking for a regular file. File
locks requested with the lockf subroutine are enforced.
- S_IRUSR
- Permits the file's owner to read it.
- S_IWUSR
- Permits the file's owner to write to it.
- S_IXUSR
- Permits the file's owner to execute it (or to search the
directory).
- S_IRGRP
- Permits the file's group to read it.
- S_IWGRP
- Permits the file's group to write to it.
- S_IXGRP
- Permits the file's group to execute it (or to search the
directory).
- S_IROTH
- Permits others to read the file.
- S_IWOTH
- Permits others to write to the file.
- S_IXOTH
- Permits others to execute the file (or to search the directory).
Other mode values exist that can be set with the mknod
subroutine but not with the chmod subroutine.
|
| Path
| Specifies the full path name of the file.
|
Upon successful completion, the
chmod subroutine and fchmod subroutines return a value
of 0. If the chmod subroutine or fchmod
subroutine is unsuccessful, a value of -1 is returned, and the
errno global variable is set to identify the error.
The chmod subroutine is
unsuccessful and the file permissions remain unchanged if one of the following
is true:
| ENOTDIR
| A component of the Path prefix is not a directory.
|
| EACCES
| Search permission is denied on a component of the Path
prefix.
|
| EFAULT
| The Path parameter points to a location outside of the
allocated address space of the process.
|
| ELOOP
| Too many symbolic links were encountered in translating the
Path parameter.
|
| ENOENT
| The named file does not exist.
|
| ENAMETOOLONG
| A component of the Path parameter exceeded 255 characters, or
the entire Path parameter exceeded 1023 characters.
|
|
The fchmod subroutine is unsuccessful and the file permissions
remain unchanged if the following is true:
|
| EBADF
| The value of the FileDescriptor parameter is not valid.
|
|
The chmod or fchmod subroutine is unsuccessful and
the access control information for a file remains unchanged if one of the
following is true:
|
| EPERM
| The effective user ID does not match the owner of the file, and the
process does not have appropriate privileges.
|
| EROFS
| The named file resides on a read-only file system.
|
| EIO
| An I/O error occurred during the operation.
|
|
If NFS is installed on your system, the chmod and
fchmod subroutines can also be unsuccessful if the following is
true:
|
| ESTALE
| The root or current directory of the process is located in a virtual file
system that has been unmounted.
|
| ETIMEDOUT
| The connection timed out.
|
Access Control: The invoker
must have search permission for all components of the Path
prefix.
If you receive the
EBUSY error, toggle the enforced locking attribute in
the Mode parameter and retry your operation. The
enforced locking attribute should never be used on a file that is
part of the Trusted Computing Base.
These subroutines are part of Base
Operating System (BOS) Runtime.
The acl_chg (acl_chg or acl_fchg Subroutine) subroutine, acl_get (acl_get or acl_fget Subroutine) subroutine, acl_put (acl_put or acl_fput Subroutine) subroutine,
acl_set (acl_set or acl_fset Subroutine) subroutine, chacl (chacl or fchacl Subroutine) subroutine, statacl subroutine, stat subroutine.
The aclget command, aclput command, chmod command.
List of Security
and Auditing Subroutines and Subroutines Overview in
AIX 5L Version 5.1 General Programming Concepts: Writing and
Debugging Programs.
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