I’ve used time
before:
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| time [some command here]
real 0m0.001s
user 0m0.001s
sys 0m0.000s
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But I never realized there is a much more verbose version than the command I have been running.
Turns out the time
I used is a Bash shell key word:
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| type time
time is a shell keyword
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I can do this instead:
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| /usr/bin/time -v [some command here]
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And this is the GNU time
command, which in its verbose (-v
) form, generates the following output:
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| User time (seconds): 0.00
System time (seconds): 0.00
Percent of CPU this job got: 100%
Elapsed (wall clock) time (h:mm:ss or m:ss): 0:00.00
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): 2976
Average resident set size (kbytes): 0
Major (requiring I/O) page faults: 0
Minor (reclaiming a frame) page faults: 147
Voluntary context switches: 1
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
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I also leared about using dd
together with /dev/urandom
as a way to generate a (potentially very large) file containing random data, as I wanted to run a process - and time it - against such a file:
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| dd if=/dev/urandom of=sample.txt bs=4M count=10
10+0 records in
10+0 records out
41943040 bytes (42 MB) copied, 0.320172 s, 131 MB/s
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If I want only human readable random data, I can use this:
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| base64 /dev/urandom | head -c 40000000 > sample.txt
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This gives me a file containing 76 characters per line.
And if I want a file with no line feeds, I can add -w0
:
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| base64 -w0 /dev/urandom | head -c 40000000 > sample.txt
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