getutent

GETUTENT(3)                Linux Programmer's Manual               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(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
       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 be-
       fore  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.  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
       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(),  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
       cause.

ERRORS
       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
       /var/run/utmp
              database of currently logged-in users

       /var/log/wtmp
              database of past user logins

ATTRIBUTES
       For  an  explanation  of  the  terms  used  in  this  section,  see at-
       tributes(7).

       +------------+---------------+------------------------------+
       |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
       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 in-
       troduces 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 pro-
       vides utmpxname(), although this function is not specified by POSIX.1.

       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
       /var/*/wtmpx.

       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
   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():
           _GNU_SOURCE
           || /* 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  functions
       return  -1.   There  are  no  utmpx equivalents of the above functions.
       (POSIX.1 does not specify such functions.)

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>
       #include <time.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
       getutmp(3), utmp(5)

COLOPHON
       This page is part of release 5.05 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

                                  2019-08-02                       GETUTENT(3)