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GETUTENT (3) | C library functions | Unix Manual Pages | :man

NAME

getutent, getutid, getutline, pututline, setutent, endutent, utmpname - access utmp file entries

CONTENTS

Synopsis
Description
Example
Files

SYNOPSIS

#include <utmp.h>

struct utmp *getutent(void);
"struct utmp *getutid(struct utmp *"ut);
"struct utmp *getutline(struct utmp *"ut);

"struct utmp *pututline(struct utmp *"ut);

void setutent(void);
void endutent(void);

"void utmpname(const char *"file);

DESCRIPTION

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.

getutid() searches forward from the current file position in the utmp file based upon ut. If ut->ut_type is 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(), getutline() and pututline() return a pointer to a static struct utmp on success, and NULL on failure.

EXAMPLE

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() and ttyname().


#include <string.h>
#include <stdlib.h>
#include <pwd.h>
#include <unistd.h>
#include <utmp.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(0)+strlen("/dev/"));
/* only correct for ptys named /dev/tty[pqr][0-9a-z] */
strcpy(entry.ut_id,ttyname(0)+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();
return 0;
}

FILES

/var/run/utmp database of currently logged-in users
/var/log/wtmp database of past user logins

"CONFORMING TO"

XPG 2, SVID 2, Linux FSSTND 1.2

In XPG2 and SVID2 the function pututline() is documented to return void, and that is what it does on many systems (AIX, HPUX, Linux libc5). HPUX introduces a new function _pututline() with the prototype given above for pututline() (also found in Linux libc5).

All these functions are obsolete now on non-Linux systems. POSIX 1003.1-2001, following XPG4.2, 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);

The utmpx structure is a superset of the utmp structure, with additional fields, and larger versions of the existing fields. The corresponding files are often /var/*/utmpx and /var/*/wtmpx.

Linux glibc on the other hand does not use utmpx since its utmp structure is already large enough. The functions getutxent etc. are aliases for getutent etc.

"SEE ALSO"

utmp(5)


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