pututline()

Write an entry in the user-information file

Synopsis:

#include <utmp.h>

void pututline( struct utmp * __utmp );

Description:

The getutent(), getutid(), getutline(), and pututline() functions each use 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 pututline() function writes out the supplied utmp structure into the utmp file. It uses getutid() to search forward for the proper place if it finds that it isn't already there. Normally, you should search for the proper entry using one of the the utmp*() routines. If so, pututline() doesn't search. If pututline() doesn't find a matching slot for the new entry, it adds a new entry to the end of the file. It returns a pointer to the utmp structure.

When called by a non-root user, pututline() invokes a setuid() root program to verify and write the entry, since the file specified in _PATH_UTMP is normally writable only by root. In this event, the ut_name field must correspond to the actual user name associated with the process; the ut_type field must be either USER_PROCESS or DEAD_PROCESS; the ut_line field must be a device-special file and be writable by the user.

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.