8

grep command options

I wanted to search my whole drive for a string. Following the accepted answer in Stack Overflow I used:

sudo time grep -rnw '/' -e 'Sony 50"'

and it took 53 Hours to process 20 GB of data on one of the fastest PCIe NVMe M.2 SSD's around; Samsung Pro 960.

grep output log

When grep processes some files it generates error messages. These can be suppressed by appending 2>/dev/null to the command. However the errors give feedback on progress being made. Some of the sample output (it won't all fit) is below:

Binary file /home/Me/.config/google-chrome/Default/Sync Data/SyncData.sqlite3 matches
grep: /sys/kernel/security/ima/policy: Permission denied
grep: /sys/kernel/slab/:dt-0000008/alloc_calls: Function not implemented
grep: /sys/kernel/slab/:dt-0000008/free_calls: Function not implemented
      (... SNIP ... 12 hours later PID 882 processed below...)
grep: /proc/882/task/922/attr/sockcreate: Invalid argument
grep: /proc/882/task/923/mem: Input/output error
      (... SNIP ... 24 hours later PID 2954 below...)
grep: /proc/2598/attr/sockcreate: Invalid argument
grep: /proc/2954/task/2954/mem: Input/output error
      (... SNIP ... 42 hours later PID 4396 below...)
grep: /proc/4389/attr/sockcreate: Invalid argument
grep: /proc/4396/task/4396/mem: Input/output error
      (... SNIP ... After 53 hours `grep` finally finishes...)
grep: /run/user/1000/gvfs: Permission denied
Command exited with non-zero status 2
97355.34user 83223.12system 53:07:40elapsed 94%CPU (0avgtext+0avgdata 31116maxresident)k
593910020inputs+0outputs (1major+10731minor)pagefaults 0swaps

grep gives impression it's frozen

Sometimes I thought grep was frozen because the screen didn't update for an hour and the hard disk light didn't flash much. However Conky tells me it is still running and taking 100% CPU on a single core, as seen in this GIF.

Of the 19.5 GiB out of 43.8 GiB being used on the Linux (Ubuntu 16.04.3 LTS) partition, half of this space, 10 GB are used by kernels. Downloading and testing kernels is my pass-time.


This test took most of my week-end plus Monday to complete.

How can I speed up grep and still get what I'm looking for?

  • 3
    It's good to know in either case, but may I ask why you would grep every single file on the machine in the first place? I find a usercase where there's actually nothing known about the file's path or name very hard to imagine – if it is, piping find's output to grep with parallel (or the slower alternative xargs) should be the way to go. – dessert Feb 12 '18 at 12:23
  • @dessert Unity via gnome-desktop displays a full monitor name Sony 50" and it isn't in xrandr which lists "DP-1". I wanted to find the file the full monitor name was stored in that gnome-desktop engine accessed. I had googled extensively for the file name with no luck. – WinEunuuchs2Unix Feb 13 '18 at 1:00
  • 1
    @WinEunuuchs2Unix even then there's not reason to grep the whole of /. /usr is a perfectly fine starting point. – muru Feb 13 '18 at 1:19
  • @muru Yes there are lots of golden nuggets to mine in /usr. In my case /usr/src slows it down but I can't figure out how to skip that with grep yet. As per the other complications with it's / handling. I need to do more testing. – WinEunuuchs2Unix Feb 13 '18 at 1:21
15

Exclude virtual file systems

Looking at the sample output log we see virtual file systems are included in the search which is an unnecessary waste of time. Drop these and other directories from the search with the --exclude-dir option. For example:

sudo time grep -rnw --exclude-dir={boot,dev,lib,media,mnt,proc,root,run,sys,/tmp,tmpfs,var} '/' -e 'Sony 50"'

When grep parses the /proc directory chain it is uselessly looking at all the process ID's which takes more than a day in my case.

Also when processing /mnt it will be looking at mounted Windows NTFS drives and USBs unnecessarily.

/media is holds the CD/DVD drive and external usb drives.

Output:

$ sudo time grep -rnw --exclude-dir={boot,dev,lib,media,mnt,proc,root,run,sys,/tmp,tmpfs,var} '/' -e 'Sony 50"'
Binary file /home/Me/.config/google-chrome/Default/Sync Data/SyncData.sqlite3 matches
11.35user 13.83system 0:56.35elapsed 44%CPU (0avgtext+0avgdata 8480maxresident)k
17369032inputs+0outputs (0major+1620minor)pagefaults 0swaps

There you go 56 Seconds instead of 50 Hours!

Note if you exclude usr (containing 6.5 GB of files in in my case) from the search it is only 8 seconds:

4.48user 1.80system 0:08.75elapsed 71%CPU (0avgtext+0avgdata 6012maxresident)k
13008964inputs+0outputs (0major+1180minor)pagefaults 0swaps

Interesting Notes

Keeping out the system directories seems to keep grep on better track and it never hits 100% CPU on a single core. Plus the hard disk light flashes constantly so you know grep is really working and not "thinking in circles".

If you don't prefix tmp with / then it will ignore any sub-directory containing tmp for example /home/Me/tmp. If you use --exclude-dir /tmp then your directory /home/Me/tmp will be searched.

If on the other hand you prefix sys with / then then /sys directory is searched and errors are reported. The same is true for /proc. So you have to use sys,proc and not prefix them with /. The same is true for other system directories I tested.

Create alias grepall

Consider setting up an alias in ~/.bashrc so you don't have to type the --exclude-dir parameter list every time:

alias grepall="grep --exclude-dir={boot,dev,lib,media,mnt,proc,root,run,sys,/tmp,tmpfs,var}"

Detailed time breakdown

This section breaks down how much time is saved by incrementally adding directories to the --exclude-dir parameter list:

  • /proc and /sys saving 52 hours
  • /media saving 3 minutes
  • /mnt saving 21 minutes
  • /usr/src (by specifying src) saving 53 seconds
  • /lib/modules (by specifying modules) saving 39 seconds

Exclude /proc and /sys directories

The /proc and /sys directories are the most time consuming, the most useless to search and generate the most errors. It's "useless" because these two directories are dynamically created at run-time and don't contain permanent files you would want to grep.

A great time savings is realize by excluding them:

$ sudo time grep -rnw --exclude-dir={proc,sys} '/' -e 'Garbage 098jfsd'
/var/log/auth.log:4653:Feb 16 17:46:20 alien sudo:     rick : TTY=pts/18 ; PWD=/home/rick/Downloads ; USER=root ; COMMAND=/usr/bin/time grep -rnw --exclude-dir=proc --exclude-dir=sys / -e Garbage 098jfsd
Binary file /var/log/journal/d7b25a27fe064cadb75a2f2f6ca7764e/system.journal matches
grep: /media/rick/S3A6550D005/hiberfil.sys: Input/output error
      (... SNIP ...)
grep: /media/rick/S3A6550D005/winproductkey: Input/output error
grep: /run/user/1000/gvfs: Permission denied
Command exited with non-zero status 2
422.43user 112.91system 26:59.03elapsed 33%CPU (0avgtext+0avgdata 31152maxresident)k
379671064inputs+0outputs (1major+10738minor)pagefaults 0swaps

Only 27 Minutes this time saving over 52 Hours!

There are still errors though. In /var directory which is also a "virtual directory" created at run time. The /run directory which contains an Android Cell Phone and the /media directory which contains an old broken laptop hard drive now connected to an USB external HDD enclosure.

Add /media to exclude list

The /media directory contains an old laptop drive connected via USB 3.0 port. Smartctl daily reports errors on the drive and doesn't have files we are looking for. We'll exclude it to save time and reduce error messages:

$ sudo time grep -rnw --exclude-dir={proc,sys,media} '/' -e 'Garbage 654asdf'
/var/log/auth.log:4664:Feb 16 18:26:27 alien sudo:     rick : TTY=pts/18 ; PWD=/home/rick/Downloads ; USER=root ; COMMAND=/usr/bin/time grep -rnw --exclude-dir=proc --exclude-dir=sys --exclude-dir=media / -e Garbage 654asdf
Binary file /var/log/journal/d7b25a27fe064cadb75a2f2f6ca7764e/system.journal matches
grep: /run/user/1000/gvfs: Permission denied
Command exited with non-zero status 2
405.51user 105.38system 23:26.89elapsed 36%CPU (0avgtext+0avgdata 30908maxresident)k
365800875inputs+0outputs (0major+10961minor)pagefaults 0swaps

Excluding the faulty hard drive connected via USB 3.0 enclosure only saved 3 minutes but reduced error messages.

Add /mnt (Windows NTFS partitions) to exclude list

The /mnt directory contains:

  • Two NTFS Windows 10 partitions (C: and E:) on an SSD with 105 GiB of data
  • One NTFS Windows 10 partition (D:) on an HDD with 42 GiB of data

There is nothing of interest in Windows so we'll exclude /mnt to save time:

$ ll /mnt
total 44
drwxr-xr-x  5 root root  4096 Nov 12 07:19 ./
drwxr-xr-x 27 root root  4096 Feb 15 20:43 ../
drwxrwxrwx  1 root root  8192 Dec 30 14:00 c/
drwxrwxrwx  1 root root  8192 Dec 30 14:31 d/
drwxrwxrwx  1 root root 20480 Jan  1 13:22 e/

$ sudo time grep -rnw --exclude-dir={proc,sys,media,mnt} '/' -e 'Garbage zx5cv7er'
/var/log/auth.log:5093:Feb 17 10:31:44 alien sudo:     rick : TTY=pts/18 ; PWD=/home/rick/Downloads ; USER=root ; COMMAND=/usr/bin/time grep -rnw --exclude-dir=proc --exclude-dir=sys --exclude-dir=media --exclude-dir=mnt / -e Garbage zx5cv7er
Binary file /var/log/journal/d7b25a27fe064cadb75a2f2f6ca7764e/system.journal matches
grep: /run/user/1000/gvfs: Permission denied
Command exited with non-zero status 2
51.50user 23.28system 2:08.85elapsed 58%CPU (0avgtext+0avgdata 15800maxresident)k
39866258inputs+0outputs (0major+6059minor)pagefaults 0swaps

Now grep only takes 2 minutes and 8 seconds. By excluding Windows 10 partitions with 147 Gib of Programs and Data saves 21.5 minutes!

Add /usr/src Linux Headers to exclude list

The /usr/src directory contains Linux Headers source code. In my case there are 20+ kernels manually installed which takes considerable space. To specify the directory though the argument used is src:

$ du -h -s /usr/src
3.2G    /usr/src

$ sudo time grep -rnw --exclude-dir={proc,sys,media,mnt,src} '/' -e 'Garbage z5cv7er'
/var/log/auth.log:5096:Feb 17 10:34:28 alien sudo:     rick : TTY=pts/18 ; PWD=/home/rick/Downloads ; USER=root ; COMMAND=/usr/bin/time grep -rnw --exclude-dir=proc --exclude-dir=sys --exclude-dir=media --exclude-dir=mnt --exclude-dir=src / -e Garbage z5cv7er
Binary file /var/log/journal/d7b25a27fe064cadb75a2f2f6ca7764e/system.journal matches
grep: /run/user/1000/gvfs: Permission denied
Command exited with non-zero status 2
44.21user 8.54system 1:15.51elapsed 69%CPU (0avgtext+0avgdata 15864maxresident)k
33754180inputs+0outputs (0major+6062minor)pagefaults 0swaps

Now grep is only taking 1 minutes and 15 seconds. Excluding /usr/src by specifying src on the --exclude-dir list saves 53 seconds.

Add /lib/modules Kernel modules to exclude list

The /lib/modules directory contains compiled Kernel Modules. To specify the directory though the argument used is modules:

$ du -h -d1 /lib/modules
285M    /lib/modules/4.14.18-041418-generic
282M    /lib/modules/4.14.14-041414-generic
     (... SNIP ...)
228M    /lib/modules/4.9.76-040976-generic
6.0G    /lib/modules

$ sudo time grep -rnw --exclude-dir={proc,sys,media,mnt,src,modules} '/' -e 'Garbage 1cv7fer'
/var/log/auth.log:5117:Feb 17 11:07:41 alien sudo:     rick : TTY=pts/18 ; PWD=/home/rick/Downloads ; USER=root ; COMMAND=/usr/bin/time grep -rnw --exclude-dir=proc --exclude-dir=sys --exclude-dir=media --exclude-dir=mnt --exclude-dir=src --exclude-dir=modules / -e Garbage 1cv7fer
Binary file /var/log/journal/d7b25a27fe064cadb75a2f2f6ca7764e/system.journal matches
grep: /run/user/1000/gvfs: Permission denied
Command exited with non-zero status 2
19.22user 5.84system 0:35.61elapsed 70%CPU (0avgtext+0avgdata 15600maxresident)k
22111388inputs+0outputs (0major+6059minor)pagefaults 0swaps

By skipping 6 GB of kernel modules, our grep time is 36 seconds. Adding /lib/modules by specifying modules in the --exclude-dir parameter saves 39 seconds.

Miscellaneous directories

Summary list of other directories:

  • /boot saves 3 seconds (but mine is exceptionally large)
  • /dev saves 3 seconds
  • /run saves 4 seconds
  • /var saves 8 seconds
  • 4
    Note that --exclude-dir=tmp will result in any tmp directory anywhere down in the directory tree to be excluded. So I'd rather recommend to explicitly list the directories from the root that are to be grepped, e.g. grep -r pattern /bin /etc /home .... – egmont Feb 12 '18 at 14:11
  • @egmont I tested tmp and sure enough it excluded /home/Me/tmp as well. This was fixed by using /tmp in ``exclude-dir. However if I used /sys` in exclude-dir then it was searched so it had to be set as sys instead. Very peculiar. Thanks for your input and I'm so glad this lengthy project is over :) – WinEunuuchs2Unix Feb 13 '18 at 0:47

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