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uuidd(8) [linux man page]

UUIDD(8)						      System Manager's Manual							  UUIDD(8)

NAME
uuidd - UUID generation daemon SYNOPSIS
uuidd [-d] [-p pidfile] [-s socketpath] [-T timeout] uuidd [-r|-t] [-n number] [-s socketpath] uuidd -k DESCRIPTION
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
-d Run uuidd in debugging mode. This prevents uuidd from running as a daemon. -k If currently a uuidd daemon is running, kill it. -n number When issuing a test request to a running uuidd, request a bulk response of number UUIDs. -p pidfile Specify the pathname where the pid file should be written. By default, the pid file is written to /var/run/uuidd/uuidd.pid. -s socketpath Specify the pathname used for the unix-domain socket used by uuidd. By default, the pathname used is /var/run/uuidd/request. This is primarily for debugging purposes, since the pathname is hard-coded in the libuuid library. -r Test uuidd by trying to connect to a running uuidd daemon and request it to return a random-based UUID. -t Test uuidd by trying to connect to a running uuidd daemon and request it to return a time-based UUID. -T timeout Specify a timeout for uuidd. If specified, then uuidd will exit after timeout seconds of inactivity. -q Turn on quiet flag. AUTHOR
The uuidd daemon was written by Theodore Ts'o <tytso@mit.edu>. AVAILABILITY
uuidd is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/. SEE ALSO
uuid(3), uuidgen(1) Linux May 2009 UUIDD(8)

Check Out this Related Man Page

UUID_GENERATE(3)						    Libuuid API 						  UUID_GENERATE(3)

NAME
uuid_generate, uuid_generate_random, uuid_generate_time, uuid_generate_time_safe - create a new unique UUID value SYNOPSIS
#include <uuid.h> void uuid_generate(uuid_t out); void uuid_generate_random(uuid_t out); void uuid_generate_time(uuid_t out); int uuid_generate_time_safe(uuid_t out); DESCRIPTION
The uuid_generate function creates a new universally unique identifier (UUID). The uuid will be generated based on high-quality randomness from /dev/urandom, if available. If it is not available, then uuid_generate will use an alternative algorithm which uses the current time, the local ethernet MAC address (if available), and random data generated using a pseudo-random generator. The uuid_generate_random function forces the use of the all-random UUID format, even if a high-quality random number generator (i.e., /dev/urandom) is not available, in which case a pseudo-random generator will be substituted. Note that the use of a pseudo-random genera- tor may compromise the uniqueness of UUIDs generated in this fashion. The uuid_generate_time function forces the use of the alternative algorithm which uses the current time and the local ethernet MAC address (if available). This algorithm used to be the default one used to generate UUID, but because of the use of the ethernet MAC address, it can leak information about when and where the UUID was generated. This can cause privacy problems in some applications, so the uuid_gener- ate function only uses this algorithm if a high-quality source of randomness is not available. To guarantee uniqueness of UUIDs generated by concurrently running processes, the uuid library uses global clock state counter (if the process has permissions to gain exclusive access to this file) and/or the uuidd daemon, if it is running already or can be spawned by the process (if installed and the process has enough permissions to run it). If neither of these two synchronization mechanisms can be used, it is theoretically possible that two con- currently running processes obtain the same UUID(s). To tell whether the UUID has been generated in a safe manner, use uuid_gener- ate_time_safe. The uuid_generate_time_safe is similar to uuid_generate_time, except that it returns a value which denotes whether any of the synchroniza- tion mechanisms (see above) has been used. The UUID is 16 bytes (128 bits) long, which gives approximately 3.4x10^38 unique values (there are approximately 10^80 elementary particles in the universe according to Carl Sagan's Cosmos). The new UUID can reasonably be considered unique among all UUIDs created on the local system, and among UUIDs created on other systems in the past and in the future. RETURN VALUE
The newly created UUID is returned in the memory location pointed to by out. uuid_generate_time_safe returns zero if the UUID has been generated in a safe manner, -1 otherwise. CONFORMING TO
OSF DCE 1.1 AUTHOR
Theodore Y. Ts'o AVAILABILITY
libuuid is part of the util-linux package since version 2.15.1 and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/. SEE ALSO
uuid(3), uuidgen(1), uuidd(8), uuid_clear(3), uuid_compare(3), uuid_copy(3), uuid_is_null(3), uuid_parse(3), uuid_time(3), uuid_unparse(3) util-linux May 2009 UUID_GENERATE(3)
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