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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |FILES |ATTRIBUTES |STANDARDS |HISTORY |NOTES |EXAMPLES |SEE ALSO |COLOPHON | |
getutent(3) Library Functions Manualgetutent(3)getutent, getutid, getutline, pututline, setutent, endutent, utmpname - access utmp file entries
Standard C library (libc,-lc)
#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 *path);
New applications should use the POSIX.1-specified "utmpx" versions of these functions; see STANDARDS.utmpname() sets the pathname of the utmp-format file for the other utmp functions to access. Ifutmpname() is not used to set the pathname 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 inutmp(5).getutid() searches forward from the current file position in the utmp file based uponut. Ifut->ut_type is one ofRUN_LVL,BOOT_TIME,NEW_TIME, orOLD_TIME,getutid() will find the first entry whoseut_type field matchesut->ut_type. Ifut->ut_type is one ofINIT_PROCESS,LOGIN_PROCESS,USER_PROCESS, orDEAD_PROCESS,getutid() will find the first entry whoseut_id field matchesut->ut_id.getutline() searches forward from the current file position in the utmp file. It scans entries whoseut_type isUSER_PROCESSorLOGIN_PROCESSand returns the first one whoseut_line field matchesut->ut_line.pututline() writes theutmp structureut into the utmp file. It usesgetutid() to search for the proper place in the file to insert the new entry. If it cannot find an appropriate slot forut,pututline() will append the new entry to the end of the file.
getutent(),getutid(), andgetutline() return a pointer to astruct utmp on success, and NULL on failure (which includes the "record not found" case). Thisstruct utmp is allocated in static storage, and may be overwritten by subsequent calls. On successpututline() returnsut; on failure, it returns NULL.utmpname() returns 0 if the new name was successfully stored, or -1 on failure. On failure, these functionserrno set to indicate the error.
ENOMEMOut of memory.ESRCHRecord not found.setutent(),pututline(), and thegetut*() functions can also fail for the reasons described inopen(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, seeattributes(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 inrace:utent signifies that if any of the functionssetutent(),getutent(),getutid(),getutline(),pututline(),utmpname(), orendutent() are used in parallel in different threads of a program, then data races could occur.
None.
XPG2, SVr4. In XPG2 and SVID 2 the functionpututline() 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 forpututline(). 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 usestruct utmpx, defined on Linux to be the same asstruct utmp. For completeness, glibc also providesutmpxname(), although this function is not specified by POSIX.1. On some other systems, theutmpx structure is a superset of theutmp 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 parallelutmpx file since itsutmp 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 forgetutent()).
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 (seefeature_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. Theubuf 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 ofgetpwuid(3) andttyname(3). #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); }getutmp(3),utmp(5)
This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17getutent(3)Pages that refer to this page:getlogin(3), getutmp(3), glob(3), login(3), procps_misc(3), updwtmp(3), wordexp(3), utmp(5)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |