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chmod
Changes file access permissions.
Syntax
#include <sys/types.h>
#include <sys/stat.h>
int chmod (const char *pathname, mode_t mode);
Parameters
pathname A pointer to a string containing the pathname of a file or
directory whose access permissions are to be modified. The
pathname must be terminated by a null character.
mode New access permissions. Access permission bits are set by
ORing any combination of the following macros:
S_IRWXU Set file owner class read, write, and execute
(if a file) or search (if a directory)
permission bits.
S_IRUSR Set file owner class read permission bit.
S_IWUSR Set file owner class write permission bit.
S_IXUSR Set file owner class execute (if a file) or
search (if a directory) permission bit.
S_IRWXG Set file group class read, write, and execute
(if a file) or search (if a directory)
permission bits.
S_IRGRP Set file group class read permission bit.
S_IWGRP Set file group class write permission bit.
S_IXGRP Set file group class execute (if a file) or
search (if a directory) permission bit.
S_IRWXO Set file other class read, write, and execute
(if a file) or search (if a directory)
permission bits.
S_IROTH Set file other class read permission bit.
S_IWOTH Set file other class write permission bit.
S_IXOTH Set file other class execute (if a file) or
search (if a directory) permission bit.
Unused bits of the mode parameter not associated with access
permissions must contain zeros, or an error occurs.
Return Values
0 Success.
-1 An error occurred. Access permission bits are not changed,
and errno is set to indicate the error condition.
Description
The chmod() function sets the file access permission bits of the file or
directory named in pathname to the bits specified in mode. Access
permissions can be modified only when one of the following conditions is
true:
* The user associated with the calling process is the file owner (a
user whose effective UID matches the UID of the file).
* The user associated with the calling process has appropriate
privileges, defined to be one of the following:
* a user whose GID matches the GID of the file and who has
the MPE/iX account manager (AM) user capability
* a user who has the MPE/iX system manager (SM) user
capability
Upon successful completion, chmod() marks for update the st_ctime time
field of the file.
Implementation Considerations
Refer to the EIMPL, EINVAL, and EFAULT error descriptions below.
The S_ISUID and S_ISGID bits are not currently supported.
Changes to file access permission bits do not affect access to pathname
through open file descriptors already associated with pathname at the
time of the chmod() call.
If bits in mode other than access permission bits are set to a nonzero
value, an error is returned and access permission bits are not changed.
Errors
If an error occurs, errno is set to one of the following values:
EACCES CAUSE The calling process does not have search permission
to a component of the pathname.
ACTION Make sure that the calling process has search
permission to all component directories in the
pathname.
EFAULT CAUSE The system detected a NULL or bad address in
attempting to use pathname, or the pathname was not
terminated by a null character.
ACTION Make sure that the pointer is correctly initialized.
EIMPL CAUSE One of the following:
* The pathname begins with two slash characters
(//).
* The unused bits of the mode parameter do not
contain zeros.
ACTION One of the following:
* Do not begin pathnames with two slash
characters (//).
* Set to zero all mode bits that are not access
permission bits.
EINVAL CAUSE The pathname parameter specified the root directory,
an MPE/iX account, or an MPE/iX group.
ACTION Do not attempt to change the access permission bits
of the root directory, an MPE/iX account, or an
MPE/iX group.
Table 4-0. (cont.)
ENAMETOOLONG CAUSE One of the following:
* The length of the pathname exceeds the
{PATH_MAX} limit (defined in the file
<limits.h>).
* A component of the pathname is longer than
{NAME_MAX} (defined in <limits.h>), and
{_POSIX_NO_TRUNC} is in effect for that
directory.
ACTION Make sure that both the component's length and the
full pathname length do not exceed the {NAME_MAX} or
{PATH_MAX} limits.
ENOENT CAUSE The specified file does not exist, or pathname points
to an empty string.
ACTION Specify an existing filename.
ENOTDIR CAUSE A component of the pathname is not a directory.
ACTION Specify a valid pathname.
EPERM CAUSE One of the following:
* The calling process does not have the MPE/iX
process handling (PH) capability.
* The calling process has outstanding switches
to CM code, has set critical mode, has
outstanding NOWAITIO, or is holding an
operating system internal resource, or the
calling process is in a Procedure Exit
handler.
ACTION One of the following:
* Link the program file with the MPE/iX PH
capability.
* Do not execute execl() when the calling
process has outstanding switches to CM code,
has set critical mode, has outstanding
NOWAITIO, or is holding an operating system
internal resource, or in a Procedure Exit
handler.
See Also
chown(), mkdir(), stat(), fstat(), <sys/stat.h>, POSIX.1 (Section 5.6.4)