GETUT(3C) INTERACTIVE UNIX System 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
The getutent, getutid, and getutline functions 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 */
} ut_exit; /* The exit status of a process
* marked as DEAD_PROCESS. */
time_t ut_time; /* time entry was made */
};
The getutent function 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.
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
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GETUT(3C) INTERACTIVE UNIX System GETUT(3C)
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.
The getutline function 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.
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. Mul-
tiple 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 per-
forming 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
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GETUT(3C) INTERACTIVE UNIX System GETUT(3C)
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
pututline uses an unbuffered non-standard write to avoid
race conditions between processes trying to modify the utmp
and wtmp files.
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