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

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

       #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);

       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 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.

       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

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

       ENOMEM Out of memory.

       ESRCH  Record not found.

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

              database of currently logged-in users

              database of past user logins

       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.

       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 existing
       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()).

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

           #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 feature_test_macros(7)):

       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
       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.  There are no utmpx equivalents of the above
       functions.  (POSIX.1 does not specify such functions.)

       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");


       getutmp(3), utmp(5)

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                                  2020-06-09                       GETUTENT(3)