getutent(3) - Linux manual page (original) (raw)
getutent(3) Library Functions Manual getutent(3)
NAME top
getutent, getutid, getutline, pututline, setutent, endutent,
utmpname - access utmp file entriesLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#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 top
New applications should use the POSIX.1-specified "utmpx" versions
of these functions; see STANDARDS.
**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)](../man5/utmp.5.html).
**getutid**() searches forward from the current file position in the
utmp file based upon _ut_. If _ut->uttype_ is one of **RUN_LVL**,
**BOOT_TIME**, **NEW_TIME**, or **OLD_TIME**, **getutid**() will find the first
entry whose _uttype_ field matches _ut->uttype_. If _ut->uttype_ is
one of **INIT_PROCESS**, **LOGIN_PROCESS**, **USER_PROCESS**, or **DEAD_PROCESS**,
**getutid**() will find the first entry whose _utid_ field matches
_ut->utid_.
**getutline**() searches forward from the current file position in the
utmp file. It scans entries whose _uttype_ is **USER_PROCESS** or
**LOGIN_PROCESS** and returns the first one whose _utline_ field
matches _ut->utline_.
**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 top
**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.
On failure, these functions _[errno](../man3/errno.3.html)_ set to indicate the error.ERRORS top
**ENOMEM** Out of memory.
**ESRCH** Record not found.
**setutent**(), **pututline**(), and the **getut***() functions can also fail
for the reasons described in [open(2)](../man2/open.2.html).FILES top
_/var/run/utmp_
database of currently logged-in users
_/var/log/wtmp_
database of past user loginsATTRIBUTES top
For an explanation of the terms used in this section, see
[attributes(7)](../man7/attributes.7.html).
┌─────────────┬───────────────┬──────────────────────────────────┐
│ **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.STANDARDS top
None.HISTORY top
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 top
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)](../man7/feature%5Ftest%5Fmacros.7.html)):
**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 top
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)](../man3/getpwuid.3.html) and
[ttyname(3)](../man3/ttyname.3.html).
#include <err.h>
#include <pwd.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <utmp.h>
int
main(void)
{
struct utmp entry;
if (system("echo before adding entry:;who") == -1)
err(EXIT_FAILURE, "system");
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"));
entry.ut_time = time(NULL);
strcpy(entry.ut_user, getpwuid(getuid())->pw_name);
memset(entry.ut_host, 0, UT_HOSTSIZE);
entry.ut_addr = 0;
setutent();
if (pututline(&entry) == NULL)
err(EXIT_FAILURE, "pututline");
if (system("echo after adding entry:;who") == -1)
err(EXIT_FAILURE, "system");
entry.ut_type = DEAD_PROCESS;
memset(entry.ut_line, 0, UT_LINESIZE);
entry.ut_time = 0;
memset(entry.ut_user, 0, UT_NAMESIZE);
setutent();
if (pututline(&entry) == NULL)
err(EXIT_FAILURE, "pututline");
if (system("echo after removing entry:;who") == -1)
err(EXIT_FAILURE, "system");
endutent();
exit(EXIT_SUCCESS);
}SEE ALSO top
[getutmp(3)](../man3/getutmp.3.html), [utmp(5)](../man5/utmp.5.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 getutent(3)
Pages that refer to this page:getlogin(3), getutmp(3), glob(3), login(3), procps_misc(3), updwtmp(3), wordexp(3), utmp(5)