如何測(cè)試Linux命令運(yùn)行時(shí)間？
在工作中，我曾寫(xiě)過(guò)一個(gè) Shell 腳本，這個(gè)腳本可以從 4 個(gè) NTP 服務(wù)器輪流獲取時(shí)間，然后將最可靠的時(shí)間設(shè)置為系統(tǒng)時(shí)間。
因?yàn)槲覀儗?duì)于時(shí)間的要求比較高，需要在短時(shí)間內(nèi)就獲取到正確的時(shí)間。所以我們就需要對(duì)這個(gè)腳本運(yùn)行時(shí)間進(jìn)行測(cè)試，看看從開(kāi)始運(yùn)行到正確設(shè)置時(shí)間需要花費(fèi)多少時(shí)間。
其實(shí)在工作中，還有很多情況下需要測(cè)試一個(gè)腳本或者程序運(yùn)行多少時(shí)間，特別是對(duì)于時(shí)間性要求比較高的系統(tǒng)更是如此。
對(duì)于時(shí)間的測(cè)試，我們可以用到一個(gè)命令：time 。下面我們就詳細(xì)看看如何使用 time 命令來(lái)對(duì)腳本/命令進(jìn)行測(cè)時(shí)。
1. time 命令基本用法
time 命令最基本的用法，就是 time + 命令 ，比如：
- $ time ping baidu.com
- PING baidu.com (123.125.114.144) 56(84) bytes of data.
- 64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=1 ttl=56 time=2.83 ms
- 64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=2 ttl=56 time=2.77 ms
- …………
- ^C
- --- baidu.com ping statistics ---
- 8 packets transmitted, 8 received, 0% packet loss, time 10818ms
- rtt min/avg/max/mdev = 2.765/2.808/2.862/0.039 ms
- real 0m11.173s
- user 0m0.004s
- sys 0m0.002s
在結(jié)果里，real 表示從我們執(zhí)行 ping 命令到最終按 ctrl+c 終止這段時(shí)間所耗費(fèi)的時(shí)間;user 及 sys 分別表示 ping 命令在用戶(hù)空間及內(nèi)核空間所運(yùn)行的時(shí)間。
2. 將時(shí)間信息寫(xiě)入文件
如果我們想把時(shí)間信息直接寫(xiě)入到文件，而不是顯示在屏幕上，那么我們可以使用 -o 選項(xiàng)，并指定寫(xiě)入的文件路徑。
- $ /usr/bin/time -o /home/alvin/time-output.txt ping baidu.com
執(zhí)行這個(gè)命令后，ping 命令的輸出結(jié)果依然會(huì)在終端里，而 time 命令的結(jié)果就寫(xiě)入到我們所指定的 time-output.txt 文件里。
-o 選項(xiàng)表示輸出文件不存在就創(chuàng)建，如果存在的話(huà)就直接覆蓋重寫(xiě)。如果我們不想覆蓋重寫(xiě)，而是想追加在文件后面，我們可以使用 -a 選項(xiàng)。
- $ /usr/bin/time -a /home/smart/time-output.txt ping linoxide.com
3. 顯示更詳細(xì)的時(shí)間信息
time 命令不帶選項(xiàng)的話(huà)，顯示的信息量比較少，如果我們想獲得更詳細(xì)的信息，那么我們可以使用 -v 選項(xiàng)。
- $ /usr/bin/time -v ping baidu.com
- PING baidu.com (123.125.114.144) 56(84) bytes of data.
- 64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=1 ttl=56 time=2.75 ms
- 64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=2 ttl=56 time=2.76 ms
- 64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=3 ttl=56 time=2.85 ms
- 64 bytes from 123.125.114.144 (123.125.114.144): icmp_seq=4 ttl=56 time=2.77 ms
- ^C
- --- baidu.com ping statistics ---
- 4 packets transmitted, 4 received, 0% packet loss, time 3300ms
- rtt min/avg/max/mdev = 2.751/2.785/2.851/0.075 ms
- Command being timed: "ping baidu.com"
- User time (seconds): 0.00
- System time (seconds): 0.00
- Percent of CPU this job got: 0%
- Elapsed (wall clock) time (h:mm:ss or m:ss): 0:03.64
- Average shared text size (kbytes): 0
- Average unshared data size (kbytes): 0
- Average stack size (kbytes): 0
- Average total size (kbytes): 0
- Maximum resident set size (kbytes): 2140
- Average resident set size (kbytes): 0
- Major (requiring I/O) page faults: 0
- Minor (reclaiming a frame) page faults: 626
- Voluntary context switches: 10
- Involuntary context switches: 0
- Swaps: 0
- File system inputs: 0
- File system outputs: 0
- Socket messages sent: 0
- Socket messages received: 0
- Signals delivered: 0
- Page size (bytes): 4096
- Exit status: 0
這個(gè)結(jié)果信息就相當(dāng)詳細(xì)了，我們可以獲取到足夠多我們所需要的信息。
4. 自定義輸出格式
默認(rèn)情況下，time 命令只輸出 real，usr，sys 三個(gè)內(nèi)容，如果我們想要個(gè)性化一些，算定義它的輸出格式，time 命令也是支持的。time 命令支持的格式有很多，如下所示：
- C - Name and command line arguments used
- D - Average size of the process's unshared data area in kilobytes
- E - Elapsed time in a clock format
- F - Number of page faults
- I - Number of file system inputs by the process
- K - Average total memory use of the process in kilobytes
- M - Maximum resident set the size of the process during the lifetime in Kilobytes
- O - Number of file system outputs by the process
- P - Percentage of CPU that the job received
- R - Number of minor or recoverable page faults
- S - Total number of CPU seconds used by the system in kernel mode
- U - Total number of CPU seconds used by user mode
- W - Number of times the process was swapped out of main memory
- X - Average amount of shared text in the process
- Z - System's page size in kilobytes
- c - Number of times the process was context-switched
- e - Elapsed real time used by the process in seconds
- k - Number of signals delivered to the process
- p - Average unshared stack size of the process in kilobytes
- r - Number of socket messages received by the process
- s - Number of socket messages sent by the process
- t - Average resident set size of the process in kilobytes
- w - Number of time the process was context-switched voluntarily
- x - Exit status of the command
如果我們想要輸出以下這樣的格式：
- Elapsed Time = 0:01:00, Inputs 2, Outputs 1
我們可以這樣自定義：
- $ /usr/bin/time -f "Elapsed Time = %E, Inputs %I, Outputs %O" ping baidu.com
- PING baidu.com (220.181.38.148) 56(84) bytes of data.
- 64 bytes from 220.181.38.148 (220.181.38.148): icmp_seq=1 ttl=54 time=1.82 ms
- 64 bytes from 220.181.38.148 (220.181.38.148): icmp_seq=2 ttl=54 time=1.86 ms
- ^C
- --- baidu.com ping statistics ---
- 4 packets transmitted, 4 received, 0% packet loss, time 3003ms
- rtt min/avg/max/mdev = 1.825/1.859/1.879/0.056 ms
- Elapsed Time = 0:03.92, Inputs 0, Outputs 0
如果你想讓輸出的結(jié)果有換行，可以在對(duì)應(yīng)的地方添加 \n ，比如：
- $ /usr/bin/time -f "Elapsed Time = %E \n Inputs %I \n Outputs %O" ping baidu.com
這樣輸出的結(jié)果就類(lèi)似于這樣：
- Elapsed Time = 0:03.92
- Inputs 0
- Outputs 0
