Which operating systems provide uptime information ?
Operating systems we can usually work out uptimes for are:
* BSD/OS
* FreeBSD [but not the default configuration in versions 3 to 4.3]
* HP-UX [recent versions]
* IRIX
* Linux on Intel x86 processor, kernel versions 2.1 to 2.5.24
* Linux on ARM, M68k, MIPS, PowerPC, S/390, SH and SPARC processors
* NetApp NetCache
* Solaris 2.6 and later
* Windows 2000
* Windows Server 2003
* Windows XP
Operating systems that do not provide uptime information include;
* AIX
* AS/400
* Compaq Tru64
* DG/UX
* Linux before kernel version 2.1
* Linux on Alpha and IA64 processors
* Linux on Intel x86 processor from kernel version 2.5.25 (see below)
* MacOS
* MacOSX
* NT3/Windows 95
* NT4/Windows 98
* NetBSD/OpenBSD
* NetWare
* OS/2
* OS/390
* SCO UNIX
* SunOS 4
* VM
Additionally HP-UX, Linux, NetApp NetCache, Solaris and recent releases of FreeBSD cycle back to zero after 497 days, exactly as if the machine had been rebooted at that precise point. Thus it is not possible to see a HP-UX, Linux or Solaris system with an uptime measurement above 497 days.
Why do some Operating Systems never show uptimes above 497 days ?
The method that Netcraft uses to determine the uptime of a server is bounded by an upper limit of 497 days for some Operating Systems (see above). It is therefore not possible to see uptimes for these systems that go beyond this upper limit. Although we could in theory attempt to compute the true uptime for OS's with this upper limit by monitoring for restarts at the expected time, we prefer not to do this as it can be inaccurate and error prone.
Why does my uptime go back to 0 after 198 days ?
The Linux TCP stack uses the low 32 bits from the system uptime timer, and this timer, in recent kernel releases, runs at 250Hz. This means that the timer value wraps around to 0 after roughly 198 days. Although we could in theory attempt to compute the true uptime for OS's with this upper limit by monitoring for restarts at the expected time, we prefer not to do this as it can be error prone.
Why do you not report uptimes for Linux 2.6 or FreeBSD 6 ?
We only report uptimes for systems where the operating system's timer runs at 100Hz or less. Because the TCP code only uses the low 32 bits of the timer, if the timer runs at say 1000Hz, the value wraps around every 49.7 days (whereas at 100Hz it wraps after 497 days). As there are large numbers of systems which have a higher uptime than this, it is not possible to report accurate uptimes for these systems.
The Linux kernel switched to a higher internal timer rate at kernel version 2.5.26. Linux 2.4 used a rate of 100Hz. Linux 2.6 used a timer at 1000Hz (some architectures were using 1000Hz before this), until the default was changed back to 250Hz in May 2006. (An explanation of the HZ setting in Linux.)
FreeBSD versions 4 and 5 used a 100Hz timer, but FreeBSD 6 has moved to a customisable timer with a default setting of 1000Hz.
So unfortunately this means that we cannot give reliable uptime figures for many Linux and FreeBSD servers.
Mac OS X does report uptime:
Last login: Tue May 12 22:51:51 on console
kyle-barkers-mac-mini-2:~ Kyle$ uptime
8:15 up 15 days, 9:24, 2 users, load averages: 0.39 0.89 0.96
kyle-barkers-mac-mini-2:~ Kyle$
It's not simply running 'uptime' but rather being able to get uptime information remotely without an account. Some say this information is useful for hacking the computer. At the very least it's useful if you found a way to crash or reboot the computer... the uptime will tell you if you're successful (versus a port block or other network failure)!
And as for other posts... My router box (WRT54G, serves NAT for all machines):
~ # uptime
20:35:21 up 205 days, 11:50, load average: 0.00, 0.00, 0.00
My server/workstation (web server, NFS server, Disk Array, shell box, print server, whole 9 yards) -- this is the 5/6- year powerred on machine that I've tried to keep running despite hardware failures,etc.:
doujima:~$ uptime
20:36:28 up 102 days, 9:36, 8 users, load average: 0.56, 0.44, 0.30
I have a demo Geode GX1 board, which is 266MHz. However I found that it's way too slow to serve as file server. My Disk Array server is a fairly hungry AthlonXP 2200+ but any slower, the disk array is not as fast as I'd like...
I've also calculated my computer's power consumption to be around $5 to 10/month to keep up 24/7/365. I don't have a Kill-A-Watt to confirm but using some cursory testing with a multimeter and some back of envelope calculations, and comparing it to my monthly electric bill, that's my estimate...
