time是我們比較常用的一個在bash終端監控程序運行的小工具，如

time sleep 2real 0m2.003s 整個程序運行耗時，從運行開始到運行結束 user 0m0.002s 程序運行過程中用戶占用的cpu時間 sys 0m0.001s 程序運行過程中系統占用的CPU時間

那如果我們想監控程序的運行內存怎么辦？我們可以調用系統的time，而不是bash的time，什么區別呢？

type time # 這是bash中的time time 是 shell 關鍵字# 這是系統的time which time /usr/bin/time

這時我們通常需要全路徑去調用，例如

# /usr/bin/time -v command /usr/bin/time -v STAR --runMode genomeGenerate --runThreadN 10 --genomeDir star_GRCh38 --genomeFastaFiles GRCh38.fa --sjdbGTFfile GRCh38.gtf

返回如下信息：

Aug 31 16:51:51 ..... started STAR run Aug 31 16:51:51 ... starting to generate Genome files Aug 31 16:51:52 ..... processing annotations GTF Aug 31 16:51:53 ... starting to sort Suffix Array. This may take a long time... Aug 31 16:51:54 ... sorting Suffix Array chunks and saving them to disk... Aug 31 16:52:10 ... loading chunks from disk, packing SA... Aug 31 16:52:13 ... finished generating suffix array Aug 31 16:52:13 ... generating Suffix Array index Aug 31 16:52:45 ... completed Suffix Array index Aug 31 16:52:45 ..... inserting junctions into the genome indices Aug 31 16:53:05 ... writing Genome to disk ... Aug 31 16:53:06 ... writing Suffix Array to disk ... Aug 31 16:53:09 ... writing SAindex to disk Aug 31 16:53:21 ..... finished successfullyCommand being timed: "STAR --runMode genomeGenerate --runThreadN 10 --genomeDir star_GRCh38 --genomeFastaFiles GRCh38.fa --sjdbGTFfile GRCh38.gtf"# 用戶占用CPU的時間User time (seconds): 191.97# 系統占用CPU的時間System time (seconds): 11.18# 用戶額CPU使用率；雖然指定了10個線程，但只達到了雙核效率，快了2倍Percent of CPU this job got: 223%# 程序從開始運行到結束的時間，人為感覺到的運行了多久Elapsed (wall clock) time (h:mm:ss or m:ss): 1:30.93 # 下面5項未做統計，都給予了0Average shared text size (kbytes): 0Average unshared data size (kbytes): 0Average stack size (kbytes): 0Average total size (kbytes): 0Average resident set size (kbytes): 0# 該進程占用的最大物理內存, 2.3GMaximum resident set size (kbytes): 2306644# 數據未讀入內存，從硬盤讀取后緩存入內存Major (requiring I/O) page faults: 0# 已讀入內存緩存區的數據Minor (reclaiming a frame) page faults: 2451338# 程序自動放棄CPU使用權的次數Voluntary context switches: 293# 程序被動放棄CPU使用權的次數Involuntary context switches: 434Swaps: 0# 總的讀寫字符數File system inputs: 0File system outputs: 6246432Socket messages sent: 0Socket messages received: 0Signals delivered: 0Page size (bytes): 4096Exit status: 0

有了這個工具，下一步就可以愉快的評估不同的軟件、數據量所使用的計算資源多少，進而指導電腦裝機了。

References

https://stackoverflow.com/questions/60779173/what-does-maximum-resident-set-size-mean

https://www.gnu.org/software/time/

https://ftp.gnu.org/gnu/time/

https://stackoverflow.com/questions/998517/problem-with-the-gnu-time-command-to-measure-memory-usage

https://superuser.com/questions/480928/is-there-any-command-like-time-but-for-memory-usage

https://stackoverflow.com/questions/131303/how-can-i-measure-the-actual-memory-usage-of-an-application-or-process

https://stackoverflow.com/questions/774556/peak-memory-usage-of-a-linux-unix-process/774601#774601

https://bugzilla.redhat.com/show_bug.cgi?id=702826

https://www.slashroot.in/linux-system-io-monitoring

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