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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(struct utmp *ut);
       struct utmp *getutline(struct utmp *ut);

       struct utmp *pututline(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 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 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.

ERRORS
       ENOMEM Out of memory.

       ESRCH  Record not found.

       setutent(), pututent(), 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

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 sys-
       tems  (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);

       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  utmpx-
       name(), 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 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
       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.)

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(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), feature_test_macros(7)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



                                  2008-06-29                       GETUTENT(3)