GETUTENT
NAME
getutent, getutid, getutline, pututline, setutent, endutent, utmpname - access utmp file entries
SYNOPSIS
#include <utmp.h>
struct utmp *getutent(void);
I struct utmp *getutid(struct utmp * ut );
I struct utmp *getutline(struct utmp * ut );
I struct utmp *pututline(struct utmp * ut );
void setutent(void);
void endutent(void);
I void utmpname(const char * file );
DESCRIPTION
R utmpname ()
sets the name of the utmp-format file for the other utmp
functions to access.
If
R utmpname ()
is not used to set the filename
before the other functions are used, they assume _PATH_UTMP, as
defined in <paths.h>.
R setutent ()
rewinds the file pointer to the beginning of the utmp file.
It is generally a Good Idea to call it before any of the other
functions.
R endutent ()
closes the utmp file.
It should be called when the user
code is done accessing the file with the other functions.
R getutent ()
reads a line from the current file position in the utmp
file.
It returns a pointer to a structure containing the fields of
the line.
R getutid ()
searches forward from the current file position in the utmp
file based upon ut.
If ut->ut_type is one of RUN_LVL,
BOOT_TIME, NEW_TIME, or OLD_TIME,
R getutid ()
will
find the first entry whose ut_type field matches ut->ut_type.
If ut->ut_type is one of INIT_PROCESS, LOGIN_PROCESS,
USER_PROCESS, or DEAD_PROCESS,
R getutid ()
will find the
first entry whose ut_id field matches ut->ut_id.
R getutline ()
searches forward from the current file position in the
utmp file.
It scans entries whose ut_type is USER_PROCESS
or LOGIN_PROCESS and returns the first one whose ut_line field
matches ut->ut_line.
R pututline ()
writes the utmp structure ut into the utmp file.
It uses
R getutid ()
to search for the proper place in the file to insert
the new entry.
If it cannot find an appropriate slot for ut,
R pututline ()
will append the new entry to the end of the file.
RETURN VALUE
R getutent (),
R getutid (),
R getutline ()
and
R pututline ()
return a pointer to a struct utmp on success, and NULL on failure.
This struct utmp is allocated in static storage, and may be
overwritten by subsequent calls.
FILES
/var/run/utmp database of currently logged-in users
/var/log/wtmp database of past user logins
CONFORMING TO
XPG2, SVr4.
In XPG2 and SVID 2 the function
R pututline ()
is documented to return void, and that is what it does on many systems
(AIX, HP-UX, Linux libc5).
HP-UX introduces a new function
R _pututline ()
with the prototype given above for
R pututline ()
(also found in Linux libc5).
All these functions are obsolete now on non-Linux systems.
POSIX.1-2001, following SUSv1,
does not have any of these functions, but instead uses
#include <utmpx.h>
struct utmpx *getutxent(void);
struct utmpx *getutxid(const struct utmpx *);
struct utmpx *getutxline(const struct utmpx *);
struct utmpx *pututxline(const struct utmpx *);
void setutxent(void);
void endutxent(void);
The utmpx structure is a superset of the utmp structure,
with additional fields, and larger versions of the existing fields.
The corresponding files are often
/var/*/utmpx
and
R /var/*/wtmpx .
Linux glibc on the other hand does not use utmpx since its
utmp structure is already large enough.
The functions getutxent
etc. are aliases for getutent etc.
NOTES
Glibc Notes
The above functions are not thread-safe.
Glibc adds reentrant versions
R #define _GNU_SOURCE /* or _SVID_SOURCE or _BSD_SOURCE */
#include <utmp.h>
I int getutent_r(struct utmp * ubuf , struct utmp ** ubufp );
I int getutid_r(struct utmp * ut ,
I struct utmp * ubuf , struct utmp ** ubufp );
I int getutline_r(struct utmp * ut ,
I struct utmp * ubuf , struct utmp ** ubufp );
These functions are GNU extensions, analogs of the functions of the
same name without the _r suffix.
The
ubuf
parameter gives these functions a place to store their result.
On success they return 0, and a pointer to the result is written in
*ubufp.
On error these functions return -1.
EXAMPLE
The following example adds and removes a utmp record, assuming it is run
from within a pseudo terminal.
For usage in a real application, you
should check the return values of
getpwuid(3)
and
ttyname(3).
#include <string.h>
#include <stdlib.h>
#include <pwd.h>
#include <unistd.h>
#include <utmp.h>
int
main(int argc, char *argv[])
{
struct utmp entry;
system("echo before adding entry:;who");
entry.ut_type = USER_PROCESS;
entry.ut_pid = getpid();
strcpy(entry.ut_line, ttyname(STDIN_FILENO) + strlen("/dev/"));
/* only correct for ptys named /dev/tty[pqr][0-9a-z] */
strcpy(entry.ut_id, ttyname(STDIN_FILENO) + strlen("/dev/tty"));
time(&entry.ut_time);
strcpy(entry.ut_user, getpwuid(getuid())->pw_name);
memset(entry.ut_host, 0, UT_HOSTSIZE);
entry.ut_addr = 0;
setutent();
pututline(&entry);
system("echo after adding entry:;who");
entry.ut_type = DEAD_PROCESS;
memset(entry.ut_line, 0, UT_LINESIZE);
entry.ut_time = 0;
memset(entry.ut_user, 0, UT_NAMESIZE);
setutent();
pututline(&entry);
system("echo after removing entry:;who");
endutent();
exit(EXIT_SUCCESS);
}
SEE ALSO
ČLÁNKY DO MAILU