Author(s): |
Joachim Metz <joachim.metz@gmail.com> |
Abstract: |
This document contains information about the utmp login records format. |
Classification: |
Public |
Keywords: |
Copyright (C) 2018, Joachim Metz <joachim.metz@gmail.com>.
Permission is granted to copy, distribute and/or modify this document under the
terms of the GNU Free Documentation License, Version 1.3 or any later version
published by the Free Software Foundation; with no Invariant Sections, no
Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included
in the section entitled "GNU Free Documentation License".| Version | Author | Date | Comments |
|---|---|---|---|
0.0.1 |
J.B. Metz |
May 2018 |
Initial version. |
0.0.2 |
J.B. Metz |
June 2018 |
Additional information about extensions (utmpx). |
The utmp login records format is used by the btmp, utmp and wtmp files.
-
utmp; contains a current status of the system, system boot time (used by uptime), user logins and logouts
-
wtmp; contains a historical status of the system
-
btmp; contains failed login attempts
There are multiple utmp file formats:
-
Linux libc5 utmp
-
Linux libc6 utmp
-
Mac OS X utmp
-
Mac OS X 10.5 utmpx
A Linux libc6 utmp file consists of:
-
one or more records
| Characteristics | Description |
|---|---|
Byte order |
litte-endian |
Date and time values |
POSIX timestamp with microseconds in UTC |
Character strings |
ASCII strings are Single Byte Character (SBC) or Multi Byte Character (MBC) string encoded with th system codepage. |
The Linux libc6 utmp recordd is 384 bytes in size and consists of:
| Offset | Size | Value | Description |
|---|---|---|---|
0 |
4 |
Type of login |
|
4 |
4 |
Process identifier (PID) |
|
8 |
32 |
Terminal |
|
40 |
4 |
Terminal indentifier |
|
44 |
32 |
Username |
|
76 |
256 |
Hostname |
|
332 |
2 |
Termination status |
|
334 |
2 |
Exit status |
|
336 |
4 |
Session |
|
340 |
4 |
Timestamp |
|
344 |
4 |
Microseconds |
|
348 |
16 |
IP address |
|
364 |
20 |
Unknown (reserved for future usage) |
| Value | Identifier | Description |
|---|---|---|
0 |
EMPTY |
Record is empty and does not contain valid information |
1 |
RUN_LVL |
Record represents a change in system run-level |
2 |
BOOT_TIME |
Time of system boot |
3 |
NEW_TIME |
Time after system clock change |
4 |
OLD_TIME |
Time before system clock change |
5 |
INIT_PROCESS |
Process spawned by init |
6 |
LOGIN_PROCESS |
Main process for user login session |
7 |
USER_PROCESS |
Process spawned by user |
8 |
DEAD_PROCESS |
Terminated process |
9 |
ACCOUNTING |
Unknown (Not implemented) |
A Mac OS X 10.5 utmpx file consists of:
-
file header
-
records
| Characteristics | Description |
|---|---|
Byte order |
litte-endian |
Date and time values |
POSIX timestamp with microseconds in UTC |
Character strings |
ASCII strings are Single Byte Character (SBC) or Multi Byte Character (MBC) string encoded with th system codepage. |
The Mac OS X 10.5 utmpx file header is 628 bytes in size and consists of:
| Offset | Size | Value | Description |
|---|---|---|---|
0 |
8 |
"utmpx-1.00" |
Signature |
8 |
288 |
0 |
Unknown (empty values) |
296 |
2 |
10 |
Type of login |
298 |
330 |
0 |
Unknown (empty values) |
The Mac OS X 10.5 utmpx record is 628 bytes in size and consists of:
| Offset | Size | Value | Description |
|---|---|---|---|
0 |
256 |
Username |
|
256 |
4 |
Terminal indentifier |
|
260 |
32 |
Terminal (tty name or line) |
|
292 |
4 |
Process identifier (PID) |
|
296 |
2 |
Type of login |
|
298 |
2 |
Unknown |
|
300 |
4 |
Timestamp |
|
304 |
4 |
Microseconds |
|
308 |
256 |
Hostname |
|
564 |
16 x 4 = 64 |
Unknown (reserved for future usage) |
|
Note
|
The first record contains little information except for the the boot time for PID 1. |
| Value | Identifier | Description |
|---|---|---|
0 |
EMPTY |
Record is empty and does not contain valid information |
1 |
RUN_LVL |
Record represents a change in system run-level |
2 |
BOOT_TIME |
Time of system boot |
3 |
OLD_TIME |
Time before system clock change |
4 |
NEW_TIME |
Time after system clock change |
5 |
INIT_PROCESS |
Process spawned by init |
6 |
LOGIN_PROCESS |
Main process for user login session |
7 |
USER_PROCESS |
Process spawned by user |
8 |
DEAD_PROCESS |
Terminated process |
9 |
ACCOUNTING |
Unknown |
10 |
SIGNATURE |
Signature, value used in file header |
11 |
SHUTDOWN_TIME |
TIme of system shutdown |
|
Note
|
That the order of OLD_TIME and NEW_TIME is reversed to that of Linux |
| Title: | Wikipedia: utmp |
|---|---|
URL: |
| Title: | utmp man page |
|---|---|
URL: |
| Title: | utmp header file |
|---|---|
URL: |
/usr/include/utmp.h |
| Title: | utmpx header file |
|---|---|
URL: |
/usr/include/utmpx.h |
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