sudoers_timestamp(5) — Linux manual page


SUDOERS_TIMESTAMP(5)       File Formats Manual      SUDOERS_TIMESTAMP(5)

NAME         top

       sudoers_timestamp — Sudoers Time Stamp Format

DESCRIPTION         top

       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 (5 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:

             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.

             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.

             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

             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

             The device number of the terminal associated with the
             session for records of type TS_TTY.

             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         top

       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         top

       sudoers(5), sudo(8)

HISTORY         top

       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:

             Support for tty-based time stamp file was added by
             appending the terminal name to the time stamp file name.

             The time stamp file was replaced by a per-user directory
             which contained any tty-based time stamp files.

             The target user name was added to the time stamp file name
             when the targetpw option was set.

             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.

             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.

             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

             Individual records are locked in the time stamp file
             instead of the entire file and the lock is held until
             authentication is complete.

             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

             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         top

       Many people have worked on sudo over the years; this version
       consists of code written primarily by:

             Todd C. Miller

       See the file in the sudo distribution
       ( for an exhaustive list
       of people who have contributed to sudo.

BUGS         top

       If you believe you have found a bug in , you can either file a
       bug report in the sudo bug database,,
       or open an issue at
       If you would prefer to use email, messages may be sent to the
       sudo-workers mailing list, (public) or
       <> (private).

       Please not report security vulnerabilities through public GitHub
       issues, Bugzilla or mailing lists.  Instead, report them via
       email to <>.  You may encrypt your message
       with PGP if you would like, using the key found at

SUPPORT         top

       Limited free support is available via the sudo-users mailing
       list, see to
       subscribe or search the archives.

DISCLAIMER         top

       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 file distributed with sudo or for complete details.

COLOPHON         top

       This page is part of the sudo (execute a command as another user)
       project.  Information about the project can be found at  If you have a bug report for this manual
       page, see ⟨⟩.  This page was obtained
       from the project's upstream Git repository
       ⟨⟩ on 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-08.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

Sudo 1.9.16                 November 26, 2023       SUDOERS_TIMESTAMP(5)