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There are the commands find and locate to search for files on the disk.

I know that find recursively processes all needed subdirectories to search files and therefore is slow but up-to-date, whereas locate uses a database that gets updated every now and then (when exactly?) to quickly show results which might be outdated though.

Are there any other differences? In which situations would one prefer the one or the other? And when does the locate database get updated usually?

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    Reference: unix.stackexchange.com/questions/60205/… – Rinzwind Sep 8 '15 at 13:54
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    manpages.ubuntu.com/manpages/trusty/man8/updatedb.8.html " updatedb is usually run daily by cron(8) to update the default database." – Rinzwind Sep 8 '15 at 13:56
  • @Rinzwind The linked U&L answer is awesome, it's a shame we can't make cross-site duplicates. But do you know more about the cronjob, when exactly will it run? After startup? At a specific time (I think I've read 1-2AM or something like that) only? What happens if it's shut down at that time? Does it start when the computer is on idle? How can I see the database's age? – Byte Commander Sep 8 '15 at 14:24
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    @ByteCommander - That's what anacron is for. I don't know if it's installed by default on desktop systems/servers, but it is on notebooks. It runs upon boot and sees if any cron jobs should have run while the system was off and runs them. It's really helpful, but can cause some issues if you have jobs scheduled far away from midnight. That can cause the job to be run upon boot and then again when the time comes up - possibly a lot less than 24 hours later (for a daily job.) – Joe Sep 10 '15 at 8:34
  • @Joe So will it run during boot and slow it down, or will it run some time after boot, or does it usually run with such a low priority that it just runs when the system is almost on idle? – Byte Commander Sep 10 '15 at 12:24
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locate is really only good for finding files and displaying them to humans. You can do a few things with it, but I wouldn't trust it enough to parse and —as you say— it's impossible to guarantee the state of the internal database, more so because it's only scheduled to run from /etc/cron.daily/mlocate, once a day!

find is live. It filters, excludes, executes. It's suitable for parsing. It can output relative paths. It can output full paths. It can do things based on attributes, not just names.

locate certainly has a place in my toolbox but it's usually right at the bottom as a last-ditch effort to find something. It's easier than find too.

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    I find locate to be much faster if I want to search my entire filesystem. And you can manually update the database using updatedb before using it. – hytromo Sep 8 '15 at 14:21
  • You know how that cronjob is exactly configured? Does it run at a specific time or when the system is on idle or n minutes after startup? Because I think I have read somewhere that it is scheduled at 1-2AM, when my machine is usually turned off. Will it never get updated then, except manually (sudo updatedb)? And is there a chance to see how old the database is? – Byte Commander Sep 8 '15 at 14:21
  • grep run-parts /etc/crontab You'll see that these are being managed through anacron (which you'll see through man anacron is more resilient to systems that aren't on all the time). From what I can see it should run it on boot instead if you miss the original cron time. – Oli Sep 8 '15 at 14:28
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    I find that locate doesn't index my removable/unmounted partitions, so if I want to find something on them, I have to use find. Of course, locate doesn't have all the amazing options that find does - like -exec command {} \; to run a command on every file found. I do like to use locate -b which restricts locate to finding files which match on the final component of the name - without the rest of the path. I often try that first because it's so fast. Also, you can run sudo updatedb any time you want to to refresh the locate database. – Joe Sep 10 '15 at 8:47
  • if you need real time search that is also somewhat easy, you can use something like ls -R | grep 'file_name.txt' – jena Aug 17 '16 at 12:31
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As much as I like Oli (which is a lot!) I disagree with him on the find command. I don't like it.

find command takes over three minutes

Take for example this simple command:

$ time find / -type f -name "mail-transport-agent.target"
find: ‘/lost+found’: Permission denied
find: ‘/etc/ssmtp’: Permission denied
find: ‘/etc/ssl/private’: Permission denied
    (... SNIP ...)
find: ‘/run/user/997’: Permission denied
find: ‘/run/sudo’: Permission denied
find: ‘/run/systemd/inaccessible’: Permission denied

real    3m40.589s
user    0m4.156s
sys     0m8.874s

It takes over three minutes for find to search everything starting from /. By default reams of error messages appear and you must search through them to find what you are looking for. Still it is better than grep to search the whole drive for a string which takes 53 hours: `grep`ing all files for a string takes a long time

I know I can fiddle with the find command's parameters to make it work better but the point here is the amount of time it takes to run.

locate command takes less than a second

Now let's use locate:

$ time locate mail-transport-agent.target
/lib/systemd/system/mail-transport-agent.target

real    0m0.816s
user    0m0.792s
sys     0m0.024s

The locate command takes less than a second!

updatedb only run once a day by default

It is true the updatedb command which updates the locate database is only run once a day by default. You can run it manually before searching for files just added by using:

$ time sudo updatedb

real    0m3.460s
user    0m0.503s
sys     0m1.167s

Although this will take 3 seconds, it's small in comparison to find command's 3+ minutes.

I've updated my sudo crontab -e to include the line at the bottom:

# m h  dom mon dow   command
  0 0  1   *   *     /bin/journalctl --vacuum-size=200M
*/5 *  *   *   *     /usr/bin/updatedb

Now every five minutes updatedb is run and locate commands database is almost always up-to-date.

But there are no attributes?

You can pipe locate output to other commands. If for example you want the file attributes you can use:

$ locate mail-transport-agent.target | xargs stat
  File: '/lib/systemd/system/mail-transport-agent.target'
  Size: 473         Blocks: 8          IO Block: 4096   regular file
Device: 10305h/66309d   Inode: 667460      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2018-03-31 18:11:55.091173104 -0600
Modify: 2017-10-27 04:11:45.000000000 -0600
Change: 2017-10-28 07:18:24.860065653 -0600
 Birth: -

Summary

I posted this answer to show the speed and ease of use of locate. I tried to address some of the command short-comings pointed out by others.

The find command needs to traverse the entire directory structure to find files. The locate command has it's own database which gives it lightning speed in comparison.

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  • @EliahKagan But the find command was scrolling through and listing all the directories and files on all the drives an partitions. It appeared to be working and I was expecting a printout at the end... Either way it wasn't about "fixing" the find command's search it was about getting the time. Running locate / display-auto-brightness takes 17 seconds and also displays every directory and file on all disks. – WinEunuuchs2Unix Mar 31 '18 at 23:49
  • @EliahKagan I understand. --regex was necessary because there were too many results returned with my search string. I'll find two new examples for find and locate and update my answer in a few minutes. – WinEunuuchs2Unix Mar 31 '18 at 23:54
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    To clarify Eliah's point, that find command means "print the filenames of all the files in the directories / and display-auto-brightness." I think you meant to use find / -name display-auto-brightness, but even that prints a lot of junk "Permission denied" errors. – wjandrea Mar 31 '18 at 23:59
  • @wjandrea Yes as I said the point wasn't to find the file, it was to time the find command. I'm rerunning tests now with valid parameters after flushing caches. Then I'll update the answer. – WinEunuuchs2Unix Apr 1 '18 at 0:07
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    @Win No, your example is still valid, and I don't think the processing time is changed much whether the file is found or not. – wjandrea Apr 1 '18 at 22:50

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