Make recursive chmod faster

Question

I have an installation script that unzips a directory, then recursively chmods its contents.

I'm surprised it takes almost 10 times the time it takes to unzip, to run the following two commands:

find $dir -type f -exec chmod a+r "{}" \;
find $dir -type d -exec chmod a+rx "{}" \;

Am I doing something wrong, is there a faster way to change the chmod of all files and directories?

One trick I use is just to do a chmod -R on everything (files & directories) then run the find to fix up the directories — jeffatrackaid, May 20 '13 at 16:58
You are doing `-exec chmod a+r "{}" \;` try `chmod a+r "{}" +` instead. The first will run the command chmod once for every directory. The later command will run chmod a few times, with a list of directories as options (ie `chmod dir1 dir2 dir3 dir4`). This means far few processes are created. — Zoredache, May 20 '13 at 17:01
Could the downvoter/closer explain what's wrong with this question? — BenMorel, May 20 '13 at 17:01
I didn't downvote, but your question probably would have been more appropriate over on unix.stackexchange.com. — Zoredache, May 20 '13 at 17:02
@Zoredache Woah, the `+` trick is blazing fast! Can you add your comment as an answer? — BenMorel, May 20 '13 at 17:08
You can try `-exec chmod a+r "{}" + \;` too, that should be faster. Duh, I'm too slow. — ott--, May 20 '13 at 17:11
@jeffatrackaid no fixup needed, see [mgorven’s answer](http://serverfault.com/a/509373/82614) — törzsmókus, Dec 16 '16 at 11:44

score 15 · Accepted Answer · answered May 20 '13 at 20:42

15

You can get rid of the find commands by using chmod's X flag:

execute/search only if the file is a directory or already has execute permission for some user (X)

This allows you to set the same permissions on files and directories, with directories additionally being executable, with a single command:

$ chmod -R a+rX $dir

answered May 20 '13 at 20:42

mgorven

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Now that's a fast alternative! Thanks for your answer. – BenMorel May 20 '13 at 21:25

score 5 · Answer 2 · answered May 20 '13 at 18:07

5

You could do the following (assumming Linux):

cd $dir
chmod -R a+r .
find . -type d -print0 | xargs -0 chmod a+x

This should be much faster than the combination of the two commands you indicated in your question.

answered May 20 '13 at 18:07

mdpc

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score 2 · Answer 3 · answered May 20 '13 at 19:44

2

Use tar instead. Specifically with the -p, --preserve-permissions, --same-permissions flag.
You won't can't directly zip it, but -z, --gzip, -j, --bzip2 or -J, --xz ought to work well enough. If you really must have zip it's only a | away.

answered May 20 '13 at 19:44

84104

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score 0 · Answer 4 · answered May 20 '13 at 17:00

0

Given your command, I'm thinking you are spending time waiting for find not chmod.

Try:

chmod -R a+r $dir

The "-R" means recursive

When you run the unzip and other commands preface them with

time

To get a measurement of the time spent for the various commands.

answered May 20 '13 at 17:00

John Kloian

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Thanks, but unfortunately this solves only half of the problem (I need a different `chmod` for directories). – BenMorel May 20 '13 at 17:09

Make recursive chmod faster

4 Answers4