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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).


              database of currently logged-in users

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


       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

       #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():
           || /* 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.)


       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>

       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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                                            2020-06-09                                GETUTENT(3)