jammy (3) getutxent.3.gz

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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).

       ┌────────────┬───────────────┬──────────────────────────────┐
       │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.

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.)

EXAMPLES

       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>

       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

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       information   about   reporting   bugs,   and   the  latest  version  of  this  page,  can  be  found  at
       https://www.kernel.org/doc/man-pages/.

                                                   2020-06-09                                        GETUTENT(3)