GETUT(3C) (C Programming Language Utilities) GETUT(3C)
NAME
getut: getutent, getutid, getutline, pututline, setutent,
endutent, utmpname - access utmp file entry
SYNOPSIS
#include <utmp.h>
struct utmp *getutent ( )
struct utmp *getutid (id)
struct utmp *id;
struct utmp *getutline (line)
struct utmp *line;
void pututline (utmp)
struct utmp *utmp;
void setutent ( )
void endutent ( )
void utmpname (file)
char *file;
DESCRIPTION
getutent, getutid and getutline each return a pointer to a
structure of the following type:
struct utmp {
char ut_user[8]; /* User login name */
char ut_id[4]; /* /etc/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 {
short e_termination; /* Process termination status */
short e_exit; /* Process exit status */
Page 1 May 1989
GETUT(3C) (C Programming Language Utilities) GETUT(3C)
} ut_exit; /* The exit status of a process
* marked as DEAD_PROCESS. */
time_t ut_time; /* time entry was made */
};
getutent reads in the next entry from a utmp-like file. If
the file is not already open, it opens it. If it reaches
the end of the file, it fails.
getutid 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,
it fails.
getutline searches forward from the current point in the
utmp file until it finds an entry of the type LOGIN_PROCESS
or USER_PROCESS which also has a ut_line string matching the
line->ut_line string. If the end of file is reached without
a match, it fails.
Pututline 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 is not already at the proper
place. It is expected that normally the user of pututline
will have searched for the proper entry using one of the
getut routines. If so, pututline will not search. If
pututline does not find a matching slot for the new entry,
it will add a new entry to the end of the file.
Setutent resets the input stream to the beginning of the
file. This should be done before each search for a new
entry if it is desired that the entire file be examined.
Endutent closes the currently open file.
Page 2 May 1989
GETUT(3C) (C Programming Language Utilities) GETUT(3C)
Utmpname allows the user to change the name of the file
examined, from /etc/utmp to any other file. It is most
often expected that this other file will be /etc/wtmp. If
the file does not exist, this will not be apparent until the
first attempt to reference the file is made. Utmpname does
not open the file. It just closes the old file if it is
currently open and saves the new file name.
FILES
/etc/utmp
/etc/wtmp
SEE ALSO
ttyslot(3C), utmp(4).
DIAGNOSTICS
A NULL pointer is returned upon failure to read, whether for
permissions or having reached the end of file, or upon
failure to write.
NOTES
The most current entry is saved in a static structure.
Multiple accesses require that it be copied before further
accesses are made. Each call to either getutid or getutline
sees the routine examine the static structure before
performing more I/O. If the contents of the static
structure match what it is searching for, it looks no
further. For this reason to use getutline to search for
multiple occurrences, it would be necessary to zero out the
static after each success, or getutline would just return
the same pointer over and over again. There is one
exception to the rule about removing the structure before
further reads are done. The implicit read done by pututline
(if it finds that it is not already at the correct place in
the file) will not 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
Page 3 May 1989
GETUT(3C) (C Programming Language Utilities) GETUT(3C)
pututline uses an unbuffered non-standard write to avoid
race conditions between processes trying to modify the utmp
and wtmp files.
Page 4 May 1989