UPDWTMP(3) Linux Programmer's Manual UPDWTMP(3)

updwtmp, logwtmp - append an entry to the wtmp file

#include <utmp.h>
void updwtmp(const char *wtmp_file, const struct utmp *ut);
void logwtmp(const char *line, const char *name, const char *host);
For logwtmp(), link with -lutil.

updwtmp() appends the utmp structure ut to the wtmp file.
logwtmp() constructs a utmp structure using line, name, host, current time and current process ID. Then it calls updwtmp() to append the structure to the wtmp file.

database of past user logins

For an explanation of the terms used in this section, see attributes(7).
Interface Attribute Value
updwtmp (), logwtmp () Thread safety MT-Unsafe sig:ALRM timer

Not in POSIX.1. Present on Solaris, NetBSD, and perhaps other systems.

For consistency with the other "utmpx" functions (see getutxent(3)), glibc provides (since version 2.1):

#include <utmpx.h>
void updwtmpx (const char *wtmpx_file, const struct utmpx *utx);

This function performs the same task as updwtmp(), but differs in that it takes a utmpx structure as its last argument.

getutxent(3), wtmp(5)
2017-09-15 GNU