linux系統中的uptime命令主要用於獲取主機運行時間和查詢linux系統負載等信息。
uptime命令可以顯示系統已經運行了多長時間，信息顯示依次爲：現在時間、系統已經運行了多長時間、目前有多少登陸用戶、系統在過去的1分鐘、5分鐘和15分鐘內的平均負載。
uptime命令用法十分簡單：直接輸入uptime即可.
另外還有一個參數 -V ，是用來查詢版本的。 (注意是大寫的字母v)
[linux @ localhost]$ uptime –V
procps version 3.2.7
[linux @ localhost]$ uptime
顯示結果爲：
10:19:04 up 257 days, 18:56, 12 users, load average: 2.10, 2.10,2.09
顯示內容說明：
10:19:04 //系統當前時間
up 257 days, 18:56 //主機已運行時間,時間越大，說明你的機器越穩定。
12 user //用戶連接數，是總連接數而不是用戶數
load average // 系統平均負載，統計最近1，5，15分鐘的系統平均負載
那麼什麼是系統平均負載呢？ 系統平均負載是指在特定時間間隔內運行隊列中的平均進程數。
如果每個CPU內核的當前活動進程數不大於3的話，那麼系統的性能是良好的。如果每個CPU內核的任務數大於5，那麼這臺機器的性能有嚴重問題。
如果你的linux主機是1個雙核CPU的話，當Load Average 爲6的時候說明機器已經被充分使用了。
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last
NAME
last, lastb - show listing of last logged in users
SYNOPSIS
last [-R ] [- num ] [ -n num ] [-adiox ] [ -f file ] [ -t YYYYMMDDHHMMSS ] [name... ] [tty... ]
lastb [-R ] [- num ] [ -n num ] [ -f file ] [-adiox ] [name... ] [tty... ]
DESCRIPTION
Last searches back through the file /var/log/wtmp (or the file designated by the -f flag) and dis-
plays a list of all users logged in (and out) since that file was created. Names of users and tty's
can be given, in which case last will show only those entries matching the arguments. Names of ttys
can be abbreviated, thus last 0 is the same as last tty0 .
When last catches a SIGINT signal (generated by the interrupt key, usually control-C) or a SIGQUIT
signal (generated by the quit key, usually control-/), last will show how far it has searched through
the file; in the case of the SIGINT signal last will then terminate.
The pseudo user reboot logs in each time the system is rebooted. Thus last reboot will show a log of
all reboots since the log file was created.
Lastb is the same as last , except that by default it shows a log of the file /var/log/btmp , which
contains all the bad login attempts.
OPTIONS
- num This is a count telling last how many lines to show.
-n num The same.
-t YYYYMMDDHHMMSS
Display the state of logins as of the specified time. This is useful, e.g., to determine eas-
ily who was logged in at a particular time -- specify that time with -t and look for "still
logged in".
-f file
Specifies a file to search other than /var/log/wtmp .
-R Suppresses the display of the hostname field.
-a Display the hostname in the last column. Useful in combination with the next flag.
-d For non-local logins, Linux stores not only the host name of the remote host but its IP number
as well. This option translates the IP number back into a hostname.
-i This option is like -d in that it displays the IP number of the remote host, but it displays
the IP number in numbers-and-dots notation.
-o Read an old-type wtmp file (written by linux-libc5 applications).
-x Display the system shutdown entries and run level changes.
NOTES
The files wtmp and btmp might not be found. The system only logs information in these files if they
are present. This is a local configuration issue. If you want the files to be used, they can be cre-
ated with a simple touch(1) command (for example, touch /var/log/wtmp ).
FILES
/var/log/wtmp
/var/log/btmp
AUTHOR
Miquel van Smoorenburg, miquels AT cistron.nl
SEE ALSO
shutdown(8) , login(1) , init(8)
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last reboot