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Part 7: Finding World Writable, Abandoned and other Abnormal Files

Often system administrators need to detect "abnormal" files (e.g., world writable files, files with no valid owner and/or group, SetUID files, files with unusual permissions, sizes, names, or dates). We already discusses a very important case of SUID/SGUID files.

Here is several simplified (usually you need to avoid traversing special filesystem and NFS mounts) but potentially useful examples:

Those examples are pretty simplistic as in "real life" you need to be able to block traversing of NFS and other non-native filesystems and avoid getting to special memory-mapped filesystems like proc. Earlier versions of GNU find were allergic to proc filesystem. Here is one useful approach described in from Wayne Pollock's Unix-Linux find Command Tutorial

As a system administrator you can use find to locate suspicious files (e.g., world writable files, files with no valid owner and/or group, SetUID files, files with unusual permissions, sizes, names, or dates). Here's a final more complex example (which I save as a shell script):

find / -noleaf -wholename '/proc' -prune \
     -o -wholename '/sys' -prune \
     -o -wholename '/dev' -prune \
     -o -wholename '/windows-C-Drive' -prune \
     -o -perm -2 ! -type l  ! -type s \
     ! \( -type d -perm -1000 \) -print

This says to search the whole system, skipping the directories /proc, /sys, /dev, and /windows-C-Drive (presumably a Windows partition on a dual-booted computer). The Gnu -noleaf option tells find not to assume all remaining mounted filesystems are Unix file systems (you might have a mounted CD for instance). The -o is the Boolean OR operator, and ! is the Boolean NOT operator (applies to the following criteria).

Another and potentially simpler and faster approach is to use -fstype type predicate. It is true if the filesystem to which the file belongs is of type type. For example on Solaris mounted local filesystems have type ufs (Solaris 10 added zfs). For AIX local filesystem is jfs or jfs2 (journalled file system).

But sometimes the same server uses several types of local filesystems (for example ext3 ). In this case you can use predicate OR and create expression that covers each used filesystem or use generic predicate local and in certain circumstances predicate mount.

Strange Files Deletion and Renaming in Shell

There may come a time that you will discover that you have somehow created a file with a strange name that cannot be removed through conventional means. This section contains some unconventional approaches that may aid in removing such files.

Files that begin with a dash can be removed by typing

    rm ./-filename
A couple other ways that may work are
    rm -- -filename
    rm - -filename
Now let's suppose that we an even nastier filename. For example there can be a file with no filename. The solution is to type
    rm -i *
This executes the rm command in interactive mode. Just answer "yes" to the query to remove the nameless file and "no" to all the other queries about the rest of the files.

Another method that can be used is to obtain the inode number of the strange file using ls:

    ls -i
and then type
    find . -inum number -ok rm '{}' \;
where number is the inode number.

The -ok flag causes a confirmation prompt to be displayed. This is for your safety in case you mistypes inode number.

If you want to rename the file with the strange name, following modification to the find command works:

    find . -inum number -ok mv '{}' new_filename \;

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[Jul 03, 2016] Strange Files Deletion and Renaming in Shell

find . -empty -type d # List of empty subdirectories of current directory.

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