getutid(3) — Linux manual page


GETUTENT(3)               Linux Programmer's Manual              GETUTENT(3)

NAME         top

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

SYNOPSIS         top

       #include <utmp.h>

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

       struct utmp *pututline(const struct utmp *ut);

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

       int utmpname(const char *file);

DESCRIPTION         top

       New applications should use the POSIX.1-specified "utmpx" versions of
       these functions; see CONFORMING TO.

       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

       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.  The definition of this structure is shown in utmp(5).

       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
       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

       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         top

       getutent(), getutid(), and getutline() return a pointer to a struct
       utmp on success, and NULL on failure (which includes the "record not
       found" case).  This struct utmp is allocated in static storage, and
       may be overwritten by subsequent calls.

       On success pututline() returns ut; on failure, it returns NULL.

       utmpname() returns 0 if the new name was successfully stored, or -1
       on failure.

       In the event of an error, these functions errno set to indicate the

ERRORS         top

       ENOMEM Out of memory.

       ESRCH  Record not found.

       setutent(), pututline(), and the getut*() functions can also fail for
       the reasons described in open(2).

FILES         top

              database of currently logged-in users

              database of past user logins

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface   Attribute     Value                        │
       │getutent()  │ Thread safety │ MT-Unsafe init race:utent    │
       │            │               │ race:utentbuf sig:ALRM timer │
       │getutid(),  │ Thread safety │ MT-Unsafe init race:utent    │
       │getutline() │               │ sig:ALRM timer               │
       │pututline() │ Thread safety │ MT-Unsafe race:utent         │
       │            │               │ sig:ALRM timer               │
       │setutent(), │ Thread safety │ MT-Unsafe race:utent         │
       │endutent(), │               │                              │
       │utmpname()  │               │                              │
       In the above table, utent in race:utent signifies that if any of the
       functions setutent(), getutent(), getutid(), getutline(),
       pututline(), utmpname(), or endutent() are used in parallel in
       different threads of a program, then data races could occur.

CONFORMING TO         top

       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).  HP-UX
       introduces a new function _pututline() with the prototype given above
       for pututline().

       All these functions are obsolete now on non-Linux systems.
       POSIX.1-2001 and POSIX.1-2008, 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);

       These functions are provided by glibc, and perform the same task as
       their equivalents without the "x", but use struct utmpx, defined on
       Linux to be the same as struct utmp.  For completeness, glibc also
       provides utmpxname(), although this function is not specified by

       On some other systems, the utmpx structure is a superset of the utmp
       structure, with additional fields, and larger versions of the exist‐
       ing fields, and parallel files are maintained, often /var/*/utmpx and

       Linux glibc on the other hand does not use a parallel utmpx file
       since its utmp structure is already large enough.  The "x" functions
       listed above are just aliases for their counterparts without the "x"
       (e.g., getutxent() is an alias for getutent()).

NOTES         top

   Glibc notes
       The above functions are not thread-safe.  Glibc adds reentrant

           #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);

       Feature Test Macro Requirements for glibc (see

       getutent_r(), getutid_r(), getutline_r():
           || /* since glibc 2.19: */ _DEFAULT_SOURCE
           || /* glibc <= 2.19: */    _SVID_SOURCE || _BSD_SOURCE

       These functions are GNU extensions, analogs of the functions of the
       same name without the _r suffix.  The ubuf argument gives these func‐
       tions a place to store their result.  On success, they return 0, and
       a pointer to the result is written in *ubufp.  On error, these func‐
       tions return -1.  There are no utmpx equivalents of the above func‐
       tions.  (POSIX.1 does not specify such functions.)

EXAMPLES         top

       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>
       #include <time.h>

       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"));
           strcpy(entry.ut_user, getpwuid(getuid())->pw_name);
           memset(entry.ut_host, 0, UT_HOSTSIZE);
           entry.ut_addr = 0;

           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);

           system("echo after removing entry:;who");


SEE ALSO         top

       getutmp(3), utmp(5)

COLOPHON         top

       This page is part of release 5.08 of the Linux man-pages project.  A
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       latest version of this page, can be found at

                                 2020-06-09                      GETUTENT(3)