getutid()

Search for an entry in the user-information file

Synopsis:

#include <utmp.h>

struct utmp * getutid( struct utmp * id );

Description:

The getutent(), getutid(), getutline(), and pututline() functions each return a pointer to a utmp structure with at least the following members:

char                 ut_user[8];    /* user login name */
char                 ut_id[4];      /* /sbin/inittab id */
                                   /* (usually line #) */
char                 ut_line[12];   /* device name (console, lnxx) */
short                ut_pid;        /* process id */
short                ut_type;       /* type of entry */
struct exit_status   ut_exit;       /* exit status of a process */
                                    /* marked as DEAD_PROCESS */
time_t               ut_time;       /* time entry was made */

The structure exit_status includes at least the following members:

short   e_termination;   /* termination status */
short   e_exit;          /* exit status */

The getutid() function searches forward from the current point in the utmp file until it finds an entry with a ut_type matching id->ut_type if the type specified is RUN_LVL, BOOT_TIME, OLD_TIME, or NEW_TIME. If the type specified in id is INIT_PROCESS, LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS, then getutid() will return a pointer to the first entry whose type is one of these four and whose ut_id field matches id->ut_id. If the end of file is reached without a match, the search fails.

Returns:

A pointer to the matching entry, or NULL if it couldn't be found.

Files:

_PATH_UTMP: Specifies the user information file.

Classification:

Unix

Safety:
Cancellation point	Yes
Interrupt handler	No
Signal handler	No
Thread	Yes

Caveats:

The most current entry is saved in a static structure. Copy it before making further accesses.

On each call to either getutid() or getutline(), the routine examines the static structure before performing more I/O. If the contents of the static structure match what it's searching for, the function looks no further. For this reason, to use getutline() to search for multiple occurrences, zero out the static area after each success, or getutline() will return the same structure over and over again.

There's one exception to the rule about emptying the structure before further reads are done: the implicit read done by pututline() (if it finds that it isn't already at the correct place in the file) doesn't hurt the contents of the static structure returned by the getutent(), getutid() or getutline() routines, if the user has just modified those contents and passed the pointer back to pututline().

These routines use buffered standard I/O for input, but pututline() uses an unbuffered nonstandard write to avoid race conditions between processes trying to modify the utmp and wtmp files.