GETUTENT(3)

NAME
getutent, getutid, getutline, pututline, setutent, endutent, utmpname - access utmp file entries

SYNOPSIS
#include <utmp.h>

struct utmp *getutent(void);
struct utmp *getutid(struct utmp *ut);
struct utmp *getutline(struct utmp *ut);

struct utmp *pututline(struct utmp *ut);

void setutent(void);
void endutent(void);

void utmpname(const char *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 functions.

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 one of 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_PROCESS, 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.

RETURN VALUE
getutent(), getutid(), getutline() and 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 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 _pututline() with the prototype given above for 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 /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

#define _GNU_SOURCE    /* or _SVID_SOURCE or _BSD_SOURCE */
#include <utmp.h>

int getutent_r(struct utmp *ubuf, struct utmp **ubufp);

int getutid_r(struct utmp *ut,
              struct utmp *ubuf, struct utmp **ubufp);

int getutline_r(struct utmp *ut,
                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(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();
    exit(EXIT_SUCCESS);
}

SEE ALSO
utmp(5), feature_test_macros(7)