getutent, getutid, getutline, pututline, setutent, endutent, utmpname - access utmp file entries
#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 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).
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.
On failure, these functions errno set to indicate the
error.
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 <pwd.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
#include <utmp.h>
int
main(void)
{
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"));
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();
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);
}