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Uptime is a measure of the time a computer system has been "up" and running. It came into use to describe the opposite of downtime, times when a system was not operational. The uptime and reliability of computer and communications facilities is sometimes measured in nines (similar to the unit of metallic purity). "Five nines" means 99.999% availability, which translates to a total downtime of approximately five minutes and fifteen seconds per year.

\	Total downtime (HH:MM:SS)
Availability	per day	per month	per year
99.999%	00:00:00.9	00:00:26	00:05:16
99.99%	00:00:09	00:04:23	00:52:36
99.9%	00:01:26	00:43:50	08:45:57
99%	00:14:24	07:18:17	87:39:30

It is often used as a measure of computer operating system reliability and stability, in that this time represents the time a computer can be left unattended without crashing, or needing to be rebooted for administrative or maintenance purposes. Conversely, long uptime may indicate negligence, because critical updates can require reboots on some platforms.

Records and comparisons

The Uptime-Project, collected data on uptimes from users until 1 March 2007, and the current record for longest uptime is 11 years, 303 days, 20 hours and 57 minutes on a computer running OpenVMS. Rumours mention in January 2008 that Iarnród Éireann had an OpenVMS machine up for 18 years,^[1] which was restarted just for Y2K tests.

Netcraft maintains the uptime records for many thousands of web hosting computers.

The uptime of a personal computer is sometimes displayed as a badge of honour on an email signature or web site/forum. This was especially true in the Windows 9x days which was considered to have low uptime, sometimes attributed to the 49.7 days GetTickCount^[2] overflow issue originally preventing uptime above 49.7 days^[3] with workarounds such as requiring technicians to perform reboot every 30 day^[4], where Windows NT and Windows 2000 users would boast of uptimes of more than 30 days, whereas many real-world Windows 9x installations crashed more often. In more recent times very long uptimes for home users with Windows NT and Windows 2000 machines are less striking because the Windows 9x line has been replaced by the Windows NT-based Windows XP.

Determining system uptime

Microsoft Windows NT

Users of Windows XP Professional, Windows Server 2003 and Windows Vista systems can type systeminfo at the Command Prompt to display all system information, including the System Up Time. Windows Vista Business 64bit does not have an "Up Time" variable but rather "System Boot Time".

C:\> systeminfo | find "Up Time"
System Up Time:            0 Days, 8 Hours, 7 Minutes, 19 Seconds

Another method works in nearly all versions of Windows, including Windows 7:

C:\> net statistics server
Server Statistics for \\COMPUTERNAME

Statistics since 8/31/2009 8:52:29 PM

{16 lines of other info deleted}

(Note that the command above shows network statistics since last boot, hence up-time can be inferred.)

Also, Microsoft provides the Uptime utility (http://technet.microsoft.com/en-us/library/cc751311.aspx):

C:\>Uptime
SYSTEMNAME has been up for: 16 day(s), 4 hour(s), 24 minute(s), 47 second(s)

UNIX and Unix-like

Users of Unix-like systems can use the uptime(1) utility to get the uptime, together with the current time, the number of users and load averages for the past 1, 5 and 15 minute intervals:

$ uptime
04:20:00 up 1337 days,  2:52, 25 users,  load average: 1.76, 1.26, 0.70

OpenVMS

Users of OpenVMS systems can type show system at the command prompt:

$ show system /noprocess
OpenVMS V7.3-2 on node JERRY  29-JAN-2008 16:32:04.67  Uptime  894 22:28:52

Showing the uptime as days then hours:minutes:seconds

References

External links

[1] OpenVMS machine up for 18 years

[2] MSDN Windows GetTickCount

[3] Windows 95 Updated Vtdapi.vxd: Fixes Hanging After 49.7 Days of Continuous Use (vtdapi95.exe)

[4] Techworld.com Operating systems news Microsoft server crash nearly causes 800-plane pile-up

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-It is often used as a measure of computer [[operating system]] reliability and stability, in that this time represents the time a computer can be left unattended without [[crash (computing)|crash]]ing, or needing to be [[reboot]]ed for administrative or maintenance purposes. Conversely, long uptime can indicate negligence, because critical updates can sometimes require reboots.
+It is often used as a measure of computer [[operating system]] reliability and stability, in that this time represents the time a computer can be left unattended without [[crash (computing)|crash]]ing, or needing to be [[reboot]]ed for administrative or maintenance purposes. Conversely, long uptime may indicate negligence, because critical updates can require reboots on some platforms.
 ==Records and comparisons==

v t e Unix command-line interface programs and shell builtins
File system	cat chattr chmod chown chgrp cksum cmp cp dd du df file fuser ln ls mkdir mv pax pwd rm rmdir split tee touch type umask
Processes	at bg crontab fg kill nice ps time
User environment	env exit logname mesg talk tput uname who write
Text processing	awk basename comm csplit cut diff dirname ed ex fold head iconv join m4 more nl paste patch printf read sed sort strings tail tr troff uniq vi wc xargs
Shell builtins	alias cd echo test unset wait
Searching	find grep
Documentation	man
Software development	ar ctags lex make nm strip yacc
Miscellaneous	bc cal expr lp od sleep true and false
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