@node utmp.h
@section @file{utmp.h}

Defines functions for login and logout (to a tty session) and for examining the
history of logins and logouts.

Documentation:
@itemize
@item
@ifinfo
@ref{Manipulating the Database,,Manipulating the User Accounting Database,libc},
@end ifinfo
@ifnotinfo
@url{https://www.gnu.org/software/libc/manual/html_node/Manipulating-the-Database.html},
@end ifnotinfo
@item
@uref{https://www.kernel.org/doc/man-pages/online/pages/man5/utmp.5.html,,man utmp}.
@end itemize

Gnulib module: utmp
@mindex utmp

Portability problems fixed by Gnulib:
@itemize
@item
This header file is missing on some platforms:
FreeBSD 14.0, mingw, MSVC 14.
@item
@code{<sys/types.h>} is a prerequisite of @code{<utmp.h>} on some platforms:
FreeBSD 8.0, OpenBSD 7.2.
@end itemize

Portability problems not fixed by Gnulib:
@itemize
@item
While some platforms have the @code{struct utmp} field @code{ut_user},
older platforms have the field @code{ut_name}.
@item
The @code{struct utmp} fields @code{ut_id}, @code{ut_pid}, @code{ut_type}
do not exist on some platforms:
macOS, old FreeBSD, NetBSD, OpenBSD, Minix.
@item
The @code{struct utmp} field @code{ut_host} does not exist on some platforms:
Solaris.
@item
The @code{struct utmp} field @code{ut_exit} does not exist on some platforms:
macOS, old FreeBSD, NetBSD, OpenBSD, Minix, Cygwin.
@item
The @code{struct utmp} field @code{ut_session} does not exist on some platforms:
macOS, old FreeBSD, NetBSD, OpenBSD, Minix, AIX, HP-UX, Solaris, Cygwin.
@item
The @code{struct utmp} field @code{ut_addr} or @code{ut_addr_v6} does not exist
on some platforms:
macOS, old FreeBSD, NetBSD, OpenBSD, Minix, AIX, Solaris.
@item
On some platforms, this API does not support timestamps past the
year 2038:
glibc 2.38 on 32-bit platforms like x86 and ARM where @code{time_t}
was historically 32 bits.
@item
@mindex year2038
@mindex year2038-recommended
On some platforms, this header misbehaves if the @code{year2038} or
@code{year2038-recommended} modules are used and the program is
configured without the @option{--disable-year2038} option.
@mindex readutmp
The @code{readutmp} module works around this problem:
glibc 2.38 on 32-bit platforms like x86 and ARM where @code{time_t}
was historically 32 bits.
@xref{Avoiding the year 2038 problem}.
@end itemize
