If you want to be a good Linux administrator, therefore you should know time command. It is used to determine how long a given command takes to run.
It is useful for testing the performance of your scripts and commands (ie helps to find execution time for shell scripts or time taken for a command to finish).
How to Use Linux time command
To use time command, just execute time with the command/program you want to run as input. Please check below example
$ time ping lpicentral.blogspot.com
output
PING lpicentral.blogspot.com (104.27.115.15) 56(84) bytes of data.
64 bytes from 104.27.115.15 (104.27.115.15): icmp_seq=1 ttl=58 time=1.77 ms
64 bytes from 104.27.115.15 (104.27.115.15): icmp_seq=2 ttl=58 time=2.12 ms
64 bytes from 104.27.115.15 (104.27.115.15): icmp_seq=3 ttl=58 time=1.65 ms
--- lpicentral.blogspot.com ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 10016ms
rtt min/avg/max/mdev = 1.118/1.476/2.124/0.362 ms
real 0m10.536s
user 0m0.002s
sys 0m0.007s
The real signifies the wall clock time the 'ping' command took from execution till termination, user and sys are the time taken by ping the user space and kernel space.
How to Make time command writes its output to a file
To write the time command output to a file instead of the print out screen, use the -o command line option, which expects a file name/path as input.
$ /usr/bin/time -o /home/smart/time-output.txt ping lpicentral.blogspot.com
Now we will display ping's output on stdout, while the time command output will be written to the text file.
Note: We used /usr/bin/time instead of time because the shell built-in time command doesn't offer the -o option.
How to appends its output to an existent file
To append the time command output to an existent file instead of overwrite it, use the -a command line option.
$ /usr/bin/time -a /home/smart/time-output.txt ping lpicentral.blogspot.com
How to get Detailed output of linux time command
We can use the -v command line option to produce detailed output.
$ time -v ping lpicentral.blogspot.com
output
Command being timed: "ping lpicentral.blogspot.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): 0:11.77
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): 3064
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 158
Voluntary context switches: 14
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
How to customizing time command output
There are a large number of formatting options as shown in the following list
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
We can use the formatting switches as follows:
$ time -f "Elapsed Time = %E, Inputs %I, Outputs %O"
The output for the above command would be something like this:
Elapsed Time = 0:01:00, Inputs 2, Outputs 1
If we want to add a new line as part of the format string use the newline character as follows:
$ time -f "Elapsed Time = %E \n Inputs %I \n Outputs %O"
Linux Time Command Versions
There are three-time command Versions, Bash, Zsh and Gnu time command. We can use the type command to determine whether time is a binary or a built-in keyword.
$ type time
output
# Bash
time is a shell keyword
# Zsh
time is a reserved word
# GNU time (sh)
time is /usr/bin/time
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