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Linux find command tips

Linux Tips by Burleson Consulting

This is an excerpt from "Easy Linux Commands" by Linux guru Jon Emmons.  You can purchase it for only $19.95 (30%-off) at this link.

The find command allows users to do a comprehensive search spanning the directory tree. find also allows the setting of more specific options to filter the search results and when you?ve found what you?re looking for find even has the option to do some work on those files.

Finding Files by Age

What if a user wants to determine if there are any really old files on their server? There are dozens of options for the find command but the first thing find requires is the path in which to look.

In this example we will change our working directory to the / (root) directory and run the find command on the working directory by giving . as the path argument. The following command sequence looks for any files that are more than 20 years, 7300 days, old.

Finding files older than 20 years

# cd /
# find ./ -mtime +7300
# cd /tmp
# ls -ld orbit-root
drwx?? 2 root root 8192 Dec 31 1969 orbit-root

By default find prints the name and path to any files which match the criteria listed. In this case it has found a file in ./tmp/orbit-root which has not been modified in more than 7300 days.

You?ve probably noticed that the date on this file is a bit suspect. While the details are unimportant it is worth understanding that anything on a Linux system with a date of December 31, 1969 or January 1, 1970 has probably lost its date and time attributes somehow. It may have also been created at some time when the system?s clock was horribly wrong.

If we wanted to search the root directory without changing our working directory we could have specified the directory in the find command like this:

# find / -mtime +7300

The command found the same file in this case but has now described it starting with / instead of ./ because that is what was used in the find command.

The following command sequence will look for some newer files. The process starts in the user?s home directory and looks for files less than three days old.

Finding Any Files Modified in the Past 3 Days

$ cd ~
$ find . -mtime -3.

Now we start to really see the power of the find command. It has identified files not only in the working directory but in a subdirectory as well! Let?s verify the findings with some ls commands:

$ ls ?alt
total 56
drwxrwxr-x 2 tclark authors 4096 Feb 3 17:45 examples
-rw??- 1 tclark tclark 8793 Feb 3 14:04 .bash_history
drwx?? 4 tclark tclark 4096 Feb 3 11:17 .
-rw??- 1 tclark tclark 1066 Feb 3 11:17 .viminfo
-rw-rw-r? 1 tclark tclark 0 Feb 3 09:00 example1.fil

$ cd examples

$ ls -alt

total 20
drwxrwxr-x 2 tclark authors 4096 Feb 3 17:45 .
-rw-rw-r? 1 tclark tclark 0 Feb 3 17:45 other.txt
-rw-rw-r? 1 tclark authors 360 Feb 3 17:44 preamble.txt
drwx?? 4 tclark tclark 4096 Feb 3 11:17 ..
-rw-r?r? 1 tclark authors 2229 Jan 13 21:35 declaration.txt
-rw-rw-r? 1 tclark presidents 1310 Jan 13 17:48 gettysburg.txt

So we see that find has turned up what we were looking for. Now we will refine our search even further.

Finding .txt Files Modified in the Past 3 Days

Sometimes we are only concerned specific files in the directory. For example, say you wrote a text file sometime in the past couple days and now you can?t remember what you called it or where you put it. Here?s one way you could find that text file without having to go through your entire system:

$ find . -name '*.txt' -mtime -3

Now you?ve got even fewer files than in the last search and you could easily identify the one you?re looking for.

Note: In Windows you can use this equivalent to the UNIX -mtime check, see equivalent of UNIX mtime for Windows


Find files by size

If a user is running short of disk space, they may want to find some large files and compress them to recover space. The following will search from the current directory and find all files larger than 10,000KB. The output has been abbreviated.

Finding Files Larger than 10,000k

# find . -size +10000k

Similarly a ? could be used in this example to find all files smaller than 10,000KB. Of course there would be quite a few of those on a Linux system.

The find command is quite flexible and accepts numerous options. We have only covered a couple of the options here but if you want to check out more of them take a look at find?s man page.

Most of find?s options can be combined to find files which meet several criteria. To do this we can just continue to list criteria like we did when finding .txt files which had been modified in the past three days.

Searching for Files and Directories

The find commandallows searching part or all of the system for files and directories based on a number of criteria.  Start off by looking for files based on their name, but also how searching on other attributes and automatically performing commands on the files can be done is seen.  Many of these methods can be combined into a single command to perform very powerful and specific searches.

Searching by Name

If you know the name of a file but not where it is on the system, you can use the find command with the -name optionto locate it. The find command expects an argument indicating where to look for files followed by one or more options that may have additional arguments.  In this example, search the whole system by specifying the location.

$ find / -name tnsnames.ora

find: /home/areader: Permission denied
find: /u01/lost+found: Permission denied
find: /dev/VolGroup00: Permission denied

The find command prints out each location where a file by the given name is found.  Every time find encounters a location that the user does not have permissions to read, a ‘Permission denied’ error is printed.  Unless you are logged in as root, you can expect to get a whole lot of these when searching the entire system.

There are two ways to avoid permission errors when searching with find.  The first is to limit the scope of the search to areas where there is read access.

$ find /u01/app/oracle -name tnsnames.ora


You should do this whenever possible as it will result in faster searches, but if you find you need to search the whole system, or at least everywhere you have read access to on the system, there is another method.  Typically, output and errors are both printed to the console and appear intermixed.  You can manipulate that and send errors to a file.  You can choose to use a file in any directory where you can write to, or you can use the special file /dev/null which causes the output to disappear.

The error output is redirected by indicating 2>/dev/null after the command.  The error output is identified as 2, and this essentially takes its output and deletes it.  The final command would look something like this.

$ find / -name tnsnames.ora 2>/dev/null


It may be tempting to use this kind of redirection often, but be careful.  This causes all errors for the given command to be omitted from the results, so it is best to use it only when it is known what is going to be ignored.

NOTE:  Typically, a directory called lost+found is seen on each partition.  If files are recovered as part of a file system check, they are put in this directory.  Only root has access to this directory, so it often gives a permission error when searching with find.

The method above works very efficiently if the entire name of a file is known, but sometimes only part of the name may be known or searching for files matching a certain pattern may be desired.  This can be accomplished with wildcards.  While there are other wildcards, the * is most frequently used and matches any string, including a blank string, in its place.

$ find /u02 -name "*.dbf"

find: /u02/lost+found: Permission denied

When searching using wildcards, the search string must be put in quotes - single or double will work.  This allows the wildcard to be passed in as part of the parameter to be interpreted by the find command rather than it being interpreted by the shell.

Searching by Other Attributes

The search commandsupports searching by practically any of the file attributes that have been covered so far in this chapter.  Here are some common examples.

Searching for Recently Modified Files

The find option -mtime allows looking for files that have been modified less than or greater than a given number of days ago.  The number of days is given after the -mtime optionand ‘-’ is specified to search for files modified less than the given number of days ago, or ‘+’ to search for files modified more than the number of days ago.  This example finds files modified within the past  day.

$ find /u01 -mtime -1

find: /u01/lost+found: Permission denied

As another example, specifying -mtime +7 will return a list of files with modification dates more than seven days ago.

Searching for Files Owned by a Specific User

Using the -user option, all files in a location owned by a specific user can be quickly identified.  To be sure of the accuracy of the results, a command like this should be run as root.

# find /home -user jemmons


Searching by File Size

The -size optionof find allows searching for files larger or smaller than a specific size.  After the -size option, the size can be specified in kilobytes (k), megabytes (M) or gigabytes (G) amongst other measures.  It is possible to search for a file of an exact size, but more likely a + needs to be used to indicate files larger than a given size or - to indicate files smaller.

$ find /u02 -size +500M

find: /u02/lost+found: Permission denied

This example searches for files larger than 500 MB.

Finding a Specific Type of File

The find command can search for specific file types using the -type option.  Types are defined in the same way they are indicated in the first column of the ls -l output with the addition of f indicating regular files.  This example finds all the symbolic links in the /u01 directory.

$ find /u01 -type l

find: /u01/lost+found: Permission denied

The -type option is not overly useful by itself but can be a good way to specify only certain file types when using other options.

Searching by Inode and Identifying Hard Links

When multiple hard linksexist for the same file, it is indicated in the second column of the ls -l output, but there is no indication where the links can be found.  The find commandoffers a couple of ways to search for multiple links to the same file.

If the inode number of a file is viewed using ls -i, then use the find command with the -inum option to search for other locations where the inode number is in use.

# ls -i gunzip

983087 gunzip

# find / -inum 983087


It is important to examine this output to make sure items from other file systems are not listed since they would not represent the same file.  A simpler way to locate hard links to a given file is using the -samefile option.  Rather than taking an inode number, this option takes a file name as an argument and identifies all file names hard linked to this file.

# find / -samefile ./gzip


Performing Commands on Search Results

The default behavior of the find command is to print out a list of files found matching the given criteria.  You can override this default and perform a specific operation on a file using the -exec option.  The syntax is a little tricky, so start with an example.

$ find /u01/app/oracle/diag/rdbms/test/TEST/trace -mtime +30 -exec rm {} \;

This command searches in the trace location for files with a modification time of greater than 30 days ago and removes them.  The rm commandis given as an argument after the -exec option.  Each time a file is found matching the search criteria, the name of the found file is substituted into the command in place of the ‘{}’ curly braces and the command is executed.  The escaped semicolon ‘\;’ indicates the end of the -exec command.

A command like this can be powerful but also very dangerous.  Great care must be taken to make sure find does not execute its command on files it was not intended for.  One way to test this type of command is to use ls -l as the command after the -exec to view the results and make sure the correct files are being found before using more destructive commands like rm with find.

Combining Search Criteria

Any of the search criteria listed above can be combined to make more specific searches possible.  The order of the options is not important as long as each option is accompanied by its own arguments.  Here is a more specific example of the find command shown above.  This goes further in specifying a pattern for the file name and the file type.

$ find /u01/app/oracle/diag/rdbms/test/TEST/trace -name "*.trm" -type f -mtime +30 -exec rm {} \;

The more specific the DBA can be with a find command the better, especially when a command is reused or run automatically through cron or at.





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