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uuidd - Man Page

UUID generation daemon

Examples (TL;DR)


uuidd [options]


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.


-C,  --cont-clock[=time]

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 the max_clock_offset. This gurantees, that a clock value of a UUID will always be within the range of the max_clock_offset.

The option -C or --cont-clock enables the feature with a default max_clock_offset of 2 hours.

The option -C<NUM>[hd] or --cont-clock=<NUM>[hd] enables the feature with a max_clock_offset of NUM seconds. In case of an appended h or d, the NUM value is read 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

Print version and exit.


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


The uuidd daemon was written by Theodore Ts’o.

See Also

uuid(3), uuidgen(1)

Reporting Bugs

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


The uuidd command is part of the util-linux package which can be downloaded from Linux Kernel Archive.

Referenced By

uuidd_selinux(8), uuid_generate(3).

2024-07-04 util-linux 2.40.2 System Administration