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       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
       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.


       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.


       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


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue                        │
       │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(3),   getutent(3),   getutid(3),   getutline(3),  pututline(3),  utmpname(3),  or
       endutent(3) are used in parallel in different threads of a program, then data races  could


       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()).


   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)


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                                            2015-08-08                                GETUTENT(3)