Home How can I exclude all "permission denied" messages from "find"?
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How can I exclude all "permission denied" messages from "find"?

Léo Léopold Hertz 준영
1#
Léo Léopold Hertz 준영 Published in 2009-04-17 21:54:07Z

I need to hide all permission denied messages from:

find . > files_and_folders

I am experimenting when such message arises. I need to gather all folders and files, to which it does not arise.

Is it possible to direct the permission levels to the files_and_folders file?

How can I hide the errors at the same time?

Community
2#
Community Reply to 2017-05-23 12:26:38Z

Note:
* This answer probably goes deeper than the use case warrants, and find 2>/dev/null may be good enough in many situations. It may still be of interest for a cross-platform perspective and for its discussion of some advanced shell techniques in the interest of finding a solution that is as robust as possible, even though the cases guarded against may be largely hypothetical.
* If your system is configured to show localized error messages, prefix the find calls below with LC_ALL=C (LC_ALL=C find ...) to ensure that English messages are reported, so that grep -v 'Permission denied' works as intended. Invariably, however, any error messages that do get displayed will then be in English as well.

If your shell is bash or zsh, there's a solution that is robust while being reasonably simple, using only POSIX-compliant find features; while bash itself is not part of POSIX, most modern Unix platforms come with it, making this solution widely portable:

find . > files_and_folders 2> >(grep -v 'Permission denied' >&2)

Note: There's a small chance that some of grep's output may arrive after find completes, because the overall command doesn't wait for the command inside >(...) to finish. In bash, you can prevent this by appending | cat to the command.

  • >(...) is a (rarely used) output process substitution that allows redirecting output (in this case, stderr output (2>) to the stdin of the command inside >(...).
    In addition to bash, and zsh, ksh supports them as well in principle, but trying to combine them with redirection from stderr, as is done here (2> >(...)), appears to be silently ignored (in ksh 93u+).

    • grep -v 'Permission denied' filters out (-v) all lines (from the find command's stderr stream) that contain the phrase Permission denied and outputs the remaining lines to stderr (>&2).

This approach is:

  • robust: grep is only applied to error messages (and not to a combination of file paths and error messages, potentially leading to false positives), and error messages other than permission-denied ones are passed through, to stderr.

  • side-effect free: find's exit code is preserved: the inability to access at least one of the filesystem items encountered results in exit code 1 (although that won't tell you whether errors other than permission-denied ones occurred (too)).


POSIX-compliant solutions:

Fully POSIX-compliant solutions either have limitations or require additional work.

If find's output is to be captured in a file anyway (or suppressed altogether), then the pipeline-based solution from Jonathan Leffler's answer is simple, robust, and POSIX-compliant:

find . 2>&1 >files_and_folders | grep -v 'Permission denied' >&2

Note that the order of the redirections matters: 2>&1 must come first.

Capturing stdout output in a file up front allows 2>&1 to send only error messages through the pipeline, which grep can then unambiguously operate on.

The only downside is that the overall exit code will be the grep command's, not find's, which in this case means: if there are no errors at all or only permission-denied errors, the exit code will be 1 (signaling failure), otherwise (errors other than permission-denied ones) 0 - which is the opposite of the intent.
That said, find's exit code is rarely used anyway, as it often conveys little information beyond fundamental failure such as passing a non-existent path.
However, the specific case of even only some of the input paths being inaccessible due to lack of permissions is reflected in find's exit code (in both GNU and BSD find): if a permissions-denied error occurs for any of the files processed, the exit code is set to 1.

The following variation addresses that:

find . 2>&1 >files_and_folders | { grep -v 'Permission denied' >&2; [ $? -eq 1 ]; }

Now, the exit code indicates whether any errors other than Permission denied occurred: 1 if so, 0 otherwise.
In other words: the exit code now reflects the true intent of the command: success (0) is reported, if no errors at all or only permission-denied errors occurred.
This is arguably even better than just passing find's exit code through, as in the solution at the top.


gniourf_gniourf in the comments proposes a (still POSIX-compliant) generalization of this solution using sophisticated redirections, which works even with the default behavior of printing the file paths to stdout:

{ find . 3>&2 2>&1 1>&3 | grep -v 'Permission denied' >&3; } 3>&2 2>&1

In short: Custom file descriptor 3 is used to temporarily swap stdout (1) and stderr (2), so that error messages alone can be piped to grep via stdout.

Without these redirections, both data (file paths) and error messages would be piped to grep via stdout, and grep would then not be able to distinguish between error message Permission denied and a (hypothetical) file whose name happens to contain the phrase Permission denied.

As in the first solution, however, the the exit code reported will be grep's, not find's, but the same fix as above can be applied.


Notes on the existing answers:

  • There are several points to note about Michael Brux's answer, find . ! -readable -prune -o -print:

    • It requires GNU find; notably, it won't work on macOS. Of course, if you only ever need the command to work with GNU find, this won't be a problem for you.

    • Some Permission denied errors may still surface: find ! -readable -prune reports such errors for the child items of directories for which the current user does have r permission, but lacks x (executable) permission. The reason is that because the directory itself is readable, -prune is not executed, and the attempt to descend into that directory then triggers the error messages. That said, the typical case is for the r permission to be missing.

    • Note: The following point is a matter of philosophy and/or specific use case, and you may decide it is not relevant to you and that the command fits your needs well, especially if simply printing the paths is all you do:

      • If you conceptualize the filtering of the permission-denied error messages a separate task that you want to be able to apply to any find command, then the opposite approach of proactively preventing permission-denied errors requires introducing "noise" into the find command, which also introduces complexity and logical pitfalls.
      • For instance, the most up-voted comment on Michael's answer (as of this writing) attempts to show how to extend the command by including a -name filter, as follows:
        find . ! -readable -prune -o -name '*.txt'
        This, however, does not work as intended, because the trailing -print action is required (an explanation can be found in this answer). Such subtleties can introduce bugs.
  • The first solution in Jonathan Leffler's answer, find . 2>/dev/null > files_and_folders, as he himself states, blindly silences all error messages (and the workaround is cumbersome and not fully robust, as he also explains). Pragmatically speaking, however, it is the simplest solution, as you may be content to assume that any and all errors would be permission-related.

  • mist's answer, sudo find . > files_and_folders, is concise and pragmatic, but ill-advised for anything other than merely printing filenames, for security reasons: because you're running as the root user, "you risk having your whole system being messed up by a bug in find or a malicious version, or an incorrect invocation which writes something unexpectedly, which could not happen if you ran this with normal privileges" (from a comment on mist's answer by tripleee).

  • The 2nd solution in viraptor's answer, find . 2>&1 | grep -v 'Permission denied' > some_file runs the risk of false positives (due to sending a mix of stdout and stderr through the pipeline), and, potentially, instead of reporting non-permission-denied errors via stderr, captures them alongside the output paths in the output file.

HelloGoodbye
3#
HelloGoodbye Reply to 2017-12-19 19:30:23Z

Use:

find . 2>/dev/null > files_and_folders

This hides not just the Permission denied errors, of course, but all error messages.

If you really want to keep other possible errors, such as too many hops on a symlink, but not the permission denied ones, then you'd probably have to take a flying guess that you don't have many files called 'permission denied' and try:

find . 2>&1 | grep -v 'Permission denied' > files_and_folders

If you strictly want to filter just standard error, you can use the more elaborate construction:

find . 2>&1 > files_and_folders | grep -v 'Permission denied' >&2

The I/O redirection on the find command is: 2>&1 > files_and_folders |. The pipe redirects standard output to the grep command and is applied first. The 2>&1 sends standard error to the same place as standard output (the pipe). The > files_and_folders sends standard output (but not standard error) to a file. The net result is that messages written to standard error are sent down the pipe and the regular output of find is written to the file. The grep filters the standard output (you can decide how selective you want it to be, and may have to change the spelling depending on locale and O/S) and the final >&2 means that the surviving error messages (written to standard output) go to standard error once more. The final redirection could be regarded as optional at the terminal, but would be a very good idea to use it in a script so that error messages appear on standard error.

There are endless variations on this theme, depending on what you want to do. This will work on any variant of Unix with any Bourne shell derivative (Bash, Korn, …) and any POSIX-compliant version of find.

If you wish to adapt to the specific version of find you have on your system, there may be alternative options available. GNU find in particular has a myriad options not available in other versions — see the currently accepted answer for one such set of options.

Jason Coco
4#
Jason Coco Reply to 2009-04-17 21:57:44Z

Redirect standard error. For instance, if you're using bash on a unix machine, you can redirect standard error to /dev/null like this:

find . 2>/dev/null >files_and_folders
Micah Smith
5#
Micah Smith Reply to 2014-07-30 18:46:48Z

Pipe stderr to /dev/null by using 2>/dev/null

find . -name '...' 2>/dev/null

viraptor
6#
viraptor Reply to 2009-04-17 22:00:10Z

Those errors are printed out to the standard error output (fd 2). To filter them out, simply redirect all errors to /dev/null:

find . 2>/dev/null > some_file

or first join stderr and stdout and then grep out those specific errors:

find . 2>&1 | grep -v 'Permission denied' > some_file
Dave Jarvis
7#
Dave Jarvis Reply to 2013-03-31 03:27:02Z

I had to use:

find / -name expect 2>/dev/null

specifying the name of what I wanted to find and then telling it to redirect all errors to /dev/null

expect being the location of the expect program I was searching for.

eykanal
8#
eykanal Reply to 2014-12-31 18:54:48Z

If you want to start search from root "/" , you will probably see output somethings like:

find: /./proc/1731/fdinfo: Permission denied
find: /./proc/2032/task/2032/fd: Permission denied

It's because of permission. To solve this:

  1. You can use sudo command: sudo find /. -name 'toBeSearched.file'. it asks super user's password, when enter the password you will see result what you really want.

  2. You can use redirect the Standard Error Output from (Generally Display/Screen) to some file and avoid seeing the error messages on the screen! redirect to a special file /dev/null :

    find /. -name 'toBeSearched.file' 2>/dev/null
    
  3. You can use redirect the Standard Error Output from (Generally Display/Screen) to Standard output (Generally Display/Screen), then pipe with grep command with -v "invert" parameter to not to see the output lines which has 'Permission denied' word pairs:

    find /. -name 'toBeSearched.file' 2>&1 | grep -v 'Permission denied'
    
Community
9#
Community Reply to 2017-04-13 12:36:27Z

You can also use the -perm and -prune predicates to avoid descending into unreadable directories (see also How do I remove "permission denied" printout statements from the find program? - Unix & Linux Stack Exchange):

find . -type d ! -perm -g+r,u+r,o+r -prune -o -print > files_and_folders
Michael Brux
10#
Michael Brux Reply to 2016-10-26 14:36:26Z

Use:

find . ! -readable -prune -o -print

or more generally

find <paths> ! -readable -prune -o <other conditions like -name> -print
  • to avoid "Permission denied"
  • AND do NOT suppress (other) error messages
  • AND get exit status 0 ("all files are processed successfully")

Works with: find (GNU findutils) 4.4.2. Background:

  • The -readable test matches readable files. The ! operator returns true, when test is false. And ! -readable matches not readable directories (&files).
  • The -prune action does not descend into directory.
  • ! -readable -prune can be translated to: if directory is not readable, do not descend into it.
  • The -readable test takes into account access control lists and other permissions artefacts which the -perm test ignores.

See also find(1) manpage for many more details.

simpleuser
11#
simpleuser Reply to 2014-09-16 00:59:49Z

To avoid just the permission denied warnings, tell find to ignore the unreadable files by pruning them from the search. Add an expression as an OR to your find, such as

find / \! -readable -prune -o -name '*.jbd' -ls

This mostly says to (match an unreadable file and prune it from the list) OR (match a name like *.jbd and display it [with ls]). (Remember that by default the expressions are AND'd together unless you use -or.) You need the -ls in the second expression or else find may add a default action to show either match, which will also show you all the unreadable files.

But if you're looking for real files on your system, there is usually no reason to look in /dev, which has many many files, so you should add an expression that excludes that directory, like:

find / -mount \! -readable -prune  -o  -path /dev -prune  -o  -name '*.jbd' -ls

So (match unreadable file and prune from list) OR (match path /dev and prune from list) OR (match file like *.jbd and display it).

mist
12#
mist Reply to 2014-12-16 12:01:46Z

use

sudo find / -name file.txt

It's stupid (because you elevate the search) and nonsecure, but far shorter to write.

Léo Léopold Hertz 준영
13#
Léo Léopold Hertz 준영 Reply to 2016-02-02 09:55:44Z

While above approaches do not address the case for Mac OS X because Mac Os X does not support -readable switch this is how you can avoid 'Permission denied' errors in your output. This might help someone.

find / -type f -name "your_pattern" 2>/dev/null.

If you're using some other command with find, for example, to find the size of files of certain pattern in a directory 2>/dev/null would still work as shown below.

find . -type f -name "your_pattern" -exec du -ch {} + 2>/dev/null | grep total$.

This will return the total size of the files of a given pattern. Note the 2>/dev/null at the end of find command.

Community
14#
Community Reply to 2017-05-23 11:47:31Z

None of the above answers worked for me. Whatever I find on Internet focuses on: hide errors. None properly handles the process return-code / exit-code. I use command find within bash scripts to locate some directories and then inspect their content. I evaluate command find success using the exit-code: a value zero works, otherwise fails.

The answer provided above by Michael Brux works sometimes. But I have one scenario in which it fails! I discovered the problem and fixed it myself. I need to prune files when:

it is a directory AND has no read access AND/OR has no execute access

See the key issue here is: AND/OR. One good suggested condition sequence I read is:

-type d ! -readable ! -executable -prune

This does not work always. This means a prune is triggered when a match is:

it is directory AND no read access AND no execute access

This sequence of expressions fails when read access is granted but no execute access is.

After some testing I realized about that and changed my shell script solution to:

nice find /home*/ -maxdepth 5 -follow \
    \( -type d -a ! \( -readable -a -executable \) \) -prune \
    -o \
    \( -type d -a -readable -a -executable -a -name "${m_find_name}" \) -print

The key here is to place the "not true" for a combined expression:

has read access AND has execute access

Otherwise it has not full access, which means: prune it. This proved to work for me in one scenario which previous suggested solutions failed.

I provide below technical details for questions in the comments section. I apologize if details are excessive.

  • ¿Why using command nice? I got the idea here. Initially I thought it would be nice to reduce process priority when looking an entire filesystem. I realized it makes no sense to me, as my script is limited to few directories. I reduced -maxdepth to 3.
  • ¿Why search within /home*/? This it not relevant for this thread. I install all applications by hand via source code compile with non privileged users (not root). They are installed within "/home". I can have multiple binaries and versions living together. I need to locate all directories, inspect and backup in a master-slave fashion. I can have more than one "/home" (several disks running within a dedicated server).
  • ¿Why using -follow? Users might create symbolic links to directories. It's usefulness depends, I need to keep record of the absolute paths found.
wjordan
15#
wjordan Reply to 2016-12-30 03:42:35Z

Simple answer:

find . > files_and_folders 2>&-

2>&- closes (-) the standard error file descriptor (2) so all error messages are silenced.

  • Exit code will still be 1 if any 'Permission denied' errors would otherwise be printed

Robust answer for GNU find:

find . -type d \! \( -readable -executable \) -prune -print -o -print > files_and_folders

Pass extra options to find that -prune (prevent descending into) but still -print any directory (-typed) that does not (\!) have both -readable and -executable permissions, or (-o) -print any other file.

  • -readable and -executable options are GNU extensions, not part of the POSIX standard
  • May still return 'Permission denied' on abnormal/corrupt files (e.g., see bug report affecting container-mounted filesystems using lxcfs < v2.0.5)

Robust answer that works with any POSIX-compatible find (GNU, OSX/BSD, etc)

{ LC_ALL=C find . 3>&2 2>&1 1>&3 > files_and_folders | grep -v 'Permission denied'; [ $? = 1 ]; } 3>&2 2>&1

Use a pipeline to pass the standard error stream to grep, removing all lines containing the 'Permission denied' string.

LC_ALL=C sets the POSIX locale using an environment variable, 3>&2 2>&1 1>&3 and 3>&2 2>&1 duplicate file descriptors to pipe the standard-error stream to grep, and [ $? = 1 ] uses [] to invert the error code returned by grep to approximate the original behavior of find.

  • Will also filter any 'Permission denied' errors due to output redirection (e.g., if the files_and_folders file itself is not writable)
Leonardo Hermoso
16#
Leonardo Hermoso Reply to 2016-12-27 04:02:43Z

You can use the grep -v invert-match

-v, --invert-match        select non-matching lines

like this:

find . > files_and_folders
cat files_and_folders | grep -v "permission denied" > files_and_folders

Should to the magic

korodani
17#
korodani Reply to 2017-05-17 12:33:28Z

You also an easy solution to put your find results in a file.

find . -name 'NameOfSearchedFile' >> results.txt

Jan aka uptech
18#
Jan aka uptech Reply to 2017-08-09 23:10:28Z

-=For MacOS=-

Make a new command using alias: just add in ~/.bash_profile line:

alias search='find / -name $file 2>/dev/null'

and in new Terminal window you can call it:

$ file=<filename or mask>; search

for example:

$ file=etc; search

Kayle Sawyer
19#
Kayle Sawyer Reply to 2018-01-16 18:13:23Z

If you are using CSH or TCSH, here is a solution:

( find . > files_and_folders ) >& /dev/null

If you want output to the terminal:

( find . > /dev/tty ) >& /dev/null

However, as the "csh-whynot" FAQ describes, you should not use CSH.

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