getutxid(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
   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.

   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
   attributes(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
   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
   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
   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)

COLOPHON

   This  page  is  part of release 4.09 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/.

                              2016-10-08                       GETUTENT(3)

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