Provided by: sudo-ldap_1.9.16p2-1ubuntu1.1_amd64 
NAME
sudoers_timestamp — Sudoers Time Stamp Format
DESCRIPTION
The sudoers plugin uses per-user-ID time stamp files for credential caching. Once a user has been
authenticated, they may use sudo without a password for a short period of time (15 minutes unless
overridden by the timestamp_timeout option). By default, sudoers uses a separate record for each
terminal, which means that a user's login sessions are authenticated separately. The timestamp_type
option can be used to select the type of time stamp record sudoers will use.
A multi-record time stamp file format was introduced in sudo 1.8.10 that uses a single file per user.
Previously, a separate file was used for each user and terminal combination unless tty-based time stamps
were disabled. The new format is extensible and records of multiple types and versions may coexist
within the same file.
All records, regardless of type or version, begin with a 16-bit version number and a 16-bit record size.
Time stamp records have the following structure:
/* Time stamp entry types */
#define TS_GLOBAL 0x01U /* not restricted by tty or ppid */
#define TS_TTY 0x02U /* restricted by tty */
#define TS_PPID 0x03U /* restricted by ppid */
#define TS_LOCKEXCL 0x04U /* special lock record */
/* Time stamp flags */
#define TS_DISABLED 0x01U /* entry disabled */
#define TS_ANYUID 0x02U /* ignore uid, only valid in key */
struct timestamp_entry {
unsigned short version; /* version number */
unsigned short size; /* entry size */
unsigned short type; /* TS_GLOBAL, TS_TTY, TS_PPID */
unsigned short flags; /* TS_DISABLED, TS_ANYUID */
uid_t auth_uid; /* uid to authenticate as */
pid_t sid; /* session ID associated with tty/ppid */
struct timespec start_time; /* session/ppid start time */
struct timespec ts; /* time stamp (CLOCK_MONOTONIC) */
union {
dev_t ttydev; /* tty device number */
pid_t ppid; /* parent pid */
} u;
};
The timestamp_entry struct fields are as follows:
version
The version number of the timestamp_entry struct. New entries are created with a version number of
2. Records with different version numbers may coexist in the same file but are not inter-operable.
size The size of the record in bytes.
type The record type, currently TS_GLOBAL, TS_TTY, or TS_PPID.
flags
Zero or more record flags which can be bit-wise ORed together. Supported flags are TS_DISABLED,
for records disabled via sudo -k and TS_ANYUID, which is used only when matching records.
auth_uid
The user-ID that was used for authentication. Depending on the value of the rootpw, runaspw and
targetpw options, the user-ID may be that of the invoking user, the root user, the default runas
user or the target user.
sid The ID of the user's terminal session, if present. The session ID is only used when matching
records of type TS_TTY.
start_time
The start time of the session leader for records of type TS_TTY or of the parent process for
records of type TS_PPID. The start_time is used to help prevent reuse of a time stamp record after
a user has logged out. Not all systems support a method to easily retrieve a process's start time.
The start_time field was added in sudoers version 1.8.22 for the second revision of the
timestamp_entry struct.
ts The actual time stamp. A monotonic time source (which does not move backward) is used if the
system supports it. Where possible, sudoers uses a monotonic timer that increments even while the
system is suspended. The value of ts is updated each time a command is run via sudo. If the
difference between ts and the current time is less than the value of the timestamp_timeout option,
no password is required.
u.ttydev
The device number of the terminal associated with the session for records of type TS_TTY.
u.ppid
The ID of the parent process for records of type TS_PPID.
The tsdump utility, included with the sudo source distribution, can be used to display the contents of a
sudoers time stamp file.
LOCKING
In sudoers versions 1.8.10 through 1.8.14, the entire time stamp file was locked for exclusive access
when reading or writing to the file. Starting in sudoers 1.8.15, individual records are locked in the
time stamp file instead of the entire file and the lock is held for a longer period of time. This scheme
is described below.
The first record in the time stamp file is of type TS_LOCKEXCL and is used as a lock record to prevent
more than one sudo process from adding a new record at the same time. Once the desired time stamp record
has been located or created (and locked), the TS_LOCKEXCL record is unlocked. The lock on the individual
time stamp record, however, is held until authentication is complete. This allows sudoers to avoid
prompting for a password multiple times when it is used more than once in a pipeline.
Records of type TS_GLOBAL cannot be locked for a long period of time since doing so would interfere with
other sudo processes. Instead, a separate lock record is used to prevent multiple sudo processes using
the same terminal (or parent process ID) from prompting for a password as the same time.
SEE ALSO
sudoers(5), sudo(8)
HISTORY
Originally, sudo used a single zero-length file per user and the file's modification time was used as the
time stamp. Later versions of sudo added restrictions on the ownership of the time stamp files and
directory as well as checks on the validity of the time stamp itself. Notable changes were introduced in
the following sudo versions:
1.4.0
Support for tty-based time stamp file was added by appending the terminal name to the time stamp
file name.
1.6.2
The time stamp file was replaced by a per-user directory which contained any tty-based time stamp
files.
1.6.3p2
The target user name was added to the time stamp file name when the targetpw option was set.
1.7.3
Information about the terminal device was stored in tty-based time stamp files for validity checks.
This included the terminal device numbers, inode number and, on systems where it was not updated
when the device was written to, the inode change time. This helped prevent reuse of the time stamp
file after logout.
1.8.6p7
The terminal session ID was added to tty-based time stamp files to prevent reuse of the time stamp
by the same user in a different terminal session. It also helped prevent reuse of the time stamp
file on systems where the terminal device's inode change time was updated by writing.
1.8.10
A new, multi-record time stamp file format was introduced that uses a single file per user. The
terminal device's change time was not included since most systems now update the change time after
a write is performed as required by POSIX.
1.8.15
Individual records are locked in the time stamp file instead of the entire file and the lock is
held until authentication is complete.
1.8.22
The start time of the terminal session leader or parent process is now stored in non-global time
stamp records. This prevents reuse of the time stamp file after logout in most cases.
Support was added for the kernel-based tty time stamps available in OpenBSD which do not use an on-
disk time stamp file.
1.9.15
Time stamp file path names are now based on the invoking user-ID instead of the user name. This
avoids problems with user names that include a path separator character.
AUTHORS
Many people have worked on sudo over the years; this version consists of code written primarily by:
Todd C. Miller
See the CONTRIBUTORS.md file in the sudo distribution (https://www.sudo.ws/about/contributors/) for an
exhaustive list of people who have contributed to sudo.
BUGS
If you believe you have found a bug in sudoers_timestamp, you can either file a bug report in the sudo
bug database, https://bugzilla.sudo.ws/, or open an issue at https://github.com/sudo-project/sudo/issues.
If you would prefer to use email, messages may be sent to the sudo-workers mailing list,
https://www.sudo.ws/mailman/listinfo/sudo-workers (public) or <sudo@sudo.ws> (private).
Please not report security vulnerabilities through public GitHub issues, Bugzilla or mailing lists.
Instead, report them via email to <Todd.Miller@sudo.ws>. You may encrypt your message with PGP if you
would like, using the key found at https://www.sudo.ws/dist/PGPKEYS.
SUPPORT
Limited free support is available via the sudo-users mailing list, see
https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
DISCLAIMER
sudo is provided “AS IS” and any express or implied warranties, including, but not limited to, the
implied warranties of merchantability and fitness for a particular purpose are disclaimed. See the
LICENSE.md file distributed with sudo or https://www.sudo.ws/about/license/ for complete details.
Sudo 1.9.16p2 November 26, 2023 SUDOERS_TIMESTAMP(5)