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

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

       #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

       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.  The definition of  this  struc‐
       ture 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  appropri‐
       ate 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  allo‐
       cated 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.

       ENOMEM Out of memory.

       ESRCH  Record not found.

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

       /var/run/utmp  database of currently logged-in users
       /var/log/wtmp  database of past user logins

       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, 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 POSIX.1.

       On some other systems, the utmpx structure is a superset of the utmp structure, with addi‐
       tional  fields,  and  larger versions of the existing fields, and parallel files are main‐
       tained, 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 coun‐
       terparts without the "x" (e.g., getutxent() is an alias for getutent()).

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

       #define _GNU_SOURCE    /* or _SVID_SOURCE or _BSD_SOURCE;
                                 see feature_test_macros(7) */
       #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  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>

       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)

       This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.

                                            2014-08-19                                GETUTENT(3)

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