Tribblix: manual page: getutent.3c

GETUTENT(3C) Standard C Library Functions GETUTENT(3C)

NAME

getutent, getutid, getutline, pututline, setutent, endutent, utmpname
- user accounting database functions

SYNOPSIS

#include <utmp.h>

struct utmp *getutent(void);

struct utmp *getutid(const struct utmp *id);

struct utmp *getutline(const struct utmp *line);

struct utmp *pututline(const struct utmp *utmp);

void setutent(void);

void endutent(void);

int utmpname(const char *file);

DESCRIPTION

These functions provide access to the user accounting database, utmp.
Entries in the database are described by the definitions and data
structures in <utmp.h>.

The utmp structure contains the following members:

char ut_user[8]; /* user login name */
char ut_id[4]; /* /etc/inittab id */
/* (usually line #) */
char ut_line[12]; /* device name (console, lnxx) */
short ut_pid; /* process id */
short ut_type; /* type of entry */
struct exit_status ut_exit; /* exit status of a process */
/* marked as DEAD_PROCESS */
time_t ut_time; /* time entry was made */

The structure exit_status includes the following members:

short e_termination; /* termination status */
short e_exit; /* exit status */

getutent()
The getutent() function reads in the next entry from a utmp database.
If the database is not already open, it opens it. If it reaches the
end of the database, it fails.

getutid()
The getutid() function searches forward from the current point in the
utmp database until it finds an entry with a ut_type matching
id->ut_type if the type specified is RUN_LVL, BOOT_TIME, DOWN_TIME,
OLD_TIME, or NEW_TIME. If the type specified in id is INIT_PROCESS,
LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS, then getutid() will
return a pointer to the first entry whose type is one of these four
and whose ut_id member matches id->ut_id. If the end of database is
reached without a match, it fails.

getutline()
The getutline() function searches forward from the current point in
the utmp database until it finds an entry of the type LOGIN_PROCESS
or ut_line string matching the line->ut_line string. If the end of
database is reached without a match, it fails.

pututline()
The pututline() function writes the supplied utmp structure into the
utmp database. It uses getutid() to search forward for the proper
place if it finds that it is not already at the proper place. It is
expected that normally the user of pututline() will have searched for
the proper entry using one of these functions. If so, pututline()
will not search. If pututline() does not find a matching slot for
the new entry, it will add a new entry to the end of the database.
It returns a pointer to the utmp structure. When called by a non-root
user, pututline() invokes a setuid() root program to verify and write
the entry, since the utmp database is normally writable only by root.
In this event, the ut_name member must correspond to the actual user
name associated with the process; the ut_type member must be either
USER_PROCESS or DEAD_PROCESS; and the ut_line member must be a device
special file and be writable by the user.

setutent()
The setutent() function resets the input stream to the beginning.
This reset should be done before each search for a new entry if it is
desired that the entire database be examined.

endutent()
The endutent() function closes the currently open database.

utmpname()
The utmpname() function allows the user to change the name of the
database file examined to another file. If the file does not exist,
this will not be apparent until the first attempt to reference the
file is made. The utmpname() function does not open the file but
closes the old file if it is currently open and saves the new file
name.

RETURN VALUES

A null pointer is returned upon failure to read, whether for
permissions or having reached the end of file, or upon failure to
write. If the file name given is longer than 79 characters,
utmpname() returns 0. Otherwise, it returns 1.

USAGE

These functions use buffered standard I/O for input, but pututline()
uses an unbuffered non-standard write to avoid race conditions
between processes trying to modify the utmp and wtmp databases.

Applications should not access the utmp and wtmp databases directly,
but should use these functions to ensure that these databases are
maintained consistently. Using these functions, however, may cause
applications to fail if user accounting data cannot be represented
properly in the utmp structure (for example, on a system where PIDs
can exceed 32767). Use the functions described on the getutxent(3C)
manual page instead.

ATTRIBUTES

NOTES

The most current entry is saved in a static structure. Multiple
accesses require that it be copied before further accesses are made.
On each call to either getutid() or getutline(), the function
examines the static structure before performing more I/O. If the
contents of the static structure match what it is searching for, it
looks no further. For this reason, to use getutline() to search for
multiple occurrences, it would be necessary to zero out the static
area after each success, or getutline() would just return the same
structure over and over again. There is one exception to the rule
about emptying the structure before further reads are done. The
implicit read done by pututline() (if it finds that it is not already
at the correct place in the file) will not hurt the contents of the
static structure returned by the getutent(), getutid() or getutline()
functions, if the user has just modified those contents and passed
the pointer back to pututline().

August 13, 2023 GETUTENT(3C)