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chown
Changes the owner and group of a file.
Syntax
#include <sys/types.h>
#include <unistd.h>
int chown (const char *pathname, uid_t owner,
gid_t group);
Parameters
pathname A pointer to a string containing the pathname of a file whose
user ID and group ID are to be modified. The pathname must be
terminated by a null character.
owner The new owner (user ID) of the file.
group The new group ID of the file.
Return Values
0 Success.
-1 An error occurred. The file's owner and group ID are not
changed, and errno is set to indicate the error condition.
Description
The chown() function changes the user ID (UID) of the specified file to
owner and the group ID (GID) of the file to group.
In order to change the UID of a file, the user associated with the
calling process must be one of the following:
* The file's account manager (a user whose GID matches the GID of
the file and who has the MPE/iX account manager (AM) user
capability). In this case, owner must specify a UID belonging to
a user assigned to the account manager's own account, and group
must specify the account manager's own effective GID.
* A system manager (a user who has the MPE/iX system manager (SM)
user capability). In this case, owner can specify any UID
existing in the user database.
In order to change the GID of a file, the user associated with the
calling process must be one of the following:
* The file owner (a user whose effective UID matches the UID of the
file). In this case, owner must specify the file's UID and group
must specify the file owner's own GID.
* A user with appropriate privileges, defined to be one of the
following:
* The file's account manager (a user whose GID matches the
GID of the file and who has the MPE/iX account manager (AM)
user capability). In this case, owner must specify the UID
of a user assigned to the account manager's own account,
and group must specify the account manager's own effective
GID.
* A system manager (a user who has the MPE/iX system manager
(SM) user capability). In this case, group can specify any
GID existing in the group database.
Upon successful completion, chown() marks for update the st_ctime time
field of the file.
Implementation Considerations
Refer to the EIMPL and EFAULT error descriptions below.
The S_ISUID and S_ISGID bits are not supported.
The {_POSIX_CHOWN_RESTRICTED} constant is always in effect for pathname.
You cannot modify the GID of the root directory, MPE/iX accounts, or
MPE/iX groups.
An object's owner, its account manager(s), and system managers have
different abilities to assign UID and GID values. A system manager (user
with MPE/iX SM capability) can specify any positive UID or GID value
defined in the user or group databases. An account manager (user with
MPE/iX AM capability) can specify the UID of any user belonging to the
account manager's account, but can only specify the GID associated with
the account manager's own effective GID. File owners lacking SM or AM
capability cannot change a file's UID, but can change a file or
directory's GID to their own effective GID.
Changing an object's file owner ID (UID) or file group ID (GID) changes
access control for that file or directory. File owners of files and
directories can also change the access permissions granted to the object.
Changing an object's UID or GID also changes the file owner or file group
referenced by $OWNER and $GROUP entries in the ACD associated with the
file or directory.
An ACD is automatically assigned to a file if the file lacks an ACD and
the group parameter specifies a different GID than the GID associated
with the MPE/iX account in which the file resides. The new ACD grants
all access to the file owner and RACD access to all others.
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 the pathname parameter, 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:
* An attempt was made to change the UID or GID
of the root directory, an MPE/iX account, an
MPE/iX group, an output spool file, or a
system-defined file.
* The pathname begins with two slash characters
(//).
ACTION One of the following:
* Do not attempt to change the UID or GID of the
root directory, an MPE/iX account, an MPE/iX
group, an output spool file, or a
system-defined file.
* Do not begin pathname with two slash
characters (//).
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.
EINVAL CAUSE The owner parameter or group parameter specified an
invalid or unsupported value.
ACTION Specify a valid and supported value.
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
chmod(), POSIX.1 (Section 5.6.5)