GETUTENT(3) Library functions GETUTENT(3)
NAME
getutent, getutid, getutline, pututline, setutent, endutent, utmpname -
access utmp file entries
SYNOPSIS
#include<utmp.h>
structutmp*getutent(void);
structutmp*getutid(structutmp*ut);
structutmp*getutline(structutmp*ut);
structutmp*pututline(structutmp*ut);
voidsetutent(void);
voidendutent(void);
voidutmpname(constchar*file);
DESCRIPTION
utmpname() sets the name of the utmp-format file for the other utmp
functions to access. If utmpname() is not used to set the filename
before the other functions are used, they assume _PATH_UTMP, as defined
in <paths.h>.
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 func-
tions.
endutent() closes the utmp file. It should be called when the user
code is done accessing the file with the other functions.
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.
getutid() searches forward from the current file position in the utmp
file based upon ut. If ut->ut_type is RUN_LVL, BOOT_TIME, NEW_TIME, or
OLD_TIME, getutid() will find the first entry whose ut_type field
matches ut->ut_type. If ut->ut_type is one of INIT_PROCESS, LOGIN_PRO-
CESS, USER_PROCESS, or DEAD_PROCESS, getutid() will find the first
entry whose ut_id field matches ut->ut_id.
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.
pututline() writes the utmp structure ut into the utmp file. It uses
getutid() to search for the proper place in the file to insert the new
entry. If it cannot find an appropriate slot for ut, pututline() will
append the new entry to the end of the file.
RETURNVALUE
getutent(), getutid(), getutline() and pututline() return a pointer to
a staticstructutmp on success, and NULL on failure.
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() and ttyname().
#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(0)+strlen("/dev/"));
/* only correct for ptys named /dev/tty[pqr][0-9a-z] */
strcpy(entry.ut_id,ttyname(0)+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();
return 0;
}
FILES
/var/run/utmp database of currently logged-in users
/var/log/wtmp database of past user logins
CONFORMINGTO
XPG 2, SVID 2, Linux FSSTND 1.2
In XPG2 and SVID2 the function pututline() is documented to return
void, and that is what it does on many systems (AIX, HPUX, Linux
libc5). HPUX introduces a new function _pututline() with the prototype
given above for pututline() (also found in Linux libc5).
All these functions are obsolete now on non-Linux systems. POSIX
1003.1-2001, following XPG4.2, does not have any of these functions,
but instead uses
#include<utmpx.h>
structutmpx*getutxent(void);
structutmpx*getutxid(conststructutmpx*);
structutmpx*getutxline(conststructutmpx*);
structutmpx*pututxline(conststructutmpx*);
voidsetutxent(void);
voidendutxent(void);
The utmpx structure is a superset of the utmp structure, with addi-
tional fields, and larger versions of the existing fields. The corre-
sponding files are often /var/*/utmpx and /var/*/wtmpx.
Linux glibc on the other hand does not use utmpx since its utmp struc-
ture is already large enough. The functions getutxent etc. are aliases
for getutent etc.
SEEALSO
utmp(5)
1996-07-25 GETUTENT(3)
Take our 
