uuidd(8) — Linux manual page

UUIDD(8)                  System Administration                  UUIDD(8)

NAME         top

       uuidd - UUID generation daemon

SYNOPSIS         top

       uuidd [options]

DESCRIPTION         top

       The uuidd daemon is used by the UUID library to generate
       universally unique identifiers (UUIDs), especially time-based
       UUIDs, in a secure and guaranteed-unique fashion, even in the face
       of large numbers of threads running on different CPUs trying to
       grab UUIDs.

OPTIONS         top

       -C, --cont-clock[=number[hd]]
           Activate continuous clock handling for time-based UUIDs. uuidd
           could use all possible clock values, beginning with the
           daemon’s start time. The optional argument can be used to set
           a value for 'max_clock_offset'. This guarantees that a clock
           value of a UUID will always be within the range of
           'max_clock_offset'.

           The option -C or --cont-clock (without an argument) enables
           the feature with a default 'max_clock_offset' of 2 hours.

           The option -Cnumber or --cont-clock=number enables the feature
           with a 'max_clock_offset' of number seconds. In case of an
           appended h or d, number is understood in hours or days. The
           minimum value is 60 seconds, the maximum value is 365 days.

       -d, --debug
           Run uuidd in debugging mode. This prevents uuidd from running
           as a daemon.

       -F, --no-fork
           Do not daemonize using a double-fork.

       -k, --kill
           If currently a uuidd daemon is running, kill it.

       -n, --uuids number
           When issuing a test request to a running uuidd, request a bulk
           response of number UUIDs.

       -P, --no-pid
           Do not create a pid file.

       -p, --pid path
           Specify the pathname where the pid file should be written. By
           default, the pid file is written to
           {runstatedir}/uuidd/uuidd.pid.

       -q, --quiet
           Suppress some failure messages.

       -r, --random
           Test uuidd by trying to connect to a running uuidd daemon and
           request it to return a random-based UUID.

       -S, --socket-activation
           Do not create a socket but instead expect it to be provided by
           the calling process. This implies --no-fork and --no-pid. This
           option is intended to be used only with systemd(1). It needs
           to be enabled with a configure option.

       -s, --socket path
           Make uuidd use this pathname for the unix-domain socket. By
           default, the pathname used is {runstatedir}/uuidd/request.
           This option is primarily for debugging purposes, since the
           pathname is hard-coded in the libuuid library.

       -T, --timeout number
           Make uuidd exit after number seconds of inactivity.

       -t, --time
           Test uuidd by trying to connect to a running uuidd daemon and
           request it to return a time-based UUID.

       -h, --help
           Display help text and exit.

       -V, --version
           Display version and exit.

EXAMPLE         top

       Start up a daemon, print 42 random keys, and then stop the daemon:

           uuidd -p /tmp/uuidd.pid -s /tmp/uuidd.socket
           uuidd -d -r -n 42 -s /tmp/uuidd.socket
           uuidd -d -k -s /tmp/uuidd.socket

AUTHOR         top

       The uuidd daemon was written by Theodore Ts’o <tytso@mit.edu>.

SEE ALSO         top

       uuid(3), uuidgen(1)

REPORTING BUGS         top

       For bug reports, use the issue tracker
       <https://github.com/util-linux/util-linux/issues>.

AVAILABILITY         top

       The uuidd command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>. This page is
       part of the util-linux (a random collection of Linux utilities)
       project. Information about the project can be found at 
       ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
       bug report for this manual page, send it to
       util-linux@vger.kernel.org. This page was obtained from the
       project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2025-08-11. (At that time, the date of the most recent commit that
       was found in the repository was 2025-08-05.) 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 man-pages@man7.org

util-linux 2.42-start-521-ec46  2025-08-09                       UUIDD(8)

Pages that refer to this page: uuid_generate(3)

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