1. Basic find command
# find -name “TestFile”

2. Find Files Using Name and Ignoring Case
# find -iname “TestFile”

3. Limit Search To Specific Directory Level Using mindepth and maxdepth
# find / -maxdepth 3 -name passwd
-maxdepth –> will go 3 directories below — / 1st; /etc 2nd; /usr/bin 3rd

# find / -mindepth 3 -maxdepth 5 -name passwd
will go 3 depths first and upto 5 — so will not disply under /; /usr; /usr/bin

4. Executing Commands on the Files Found by the Find Command.
user -exec {} /;
# find -iname “TestFile” -exec md5sum {} \;

5. Inverting the match.
To inver the match use the “-not” switch
# find / -not -iname “TestFile”

6. List inodes of the files
# ls -i1 test*
16187429 test-file-name
16187430 test-file-name

# find -inum 16187430 -exec mv {} new-test-file-name \;
# ls -i1 *test*
16187430 new-test-file-name
16187429 test-file-name

7. Find file based on the File-Permissions
You can :
* Find files that match exact permission
* Check whether the given permission matches, irrespective of other permission bits
* Search by giving octal / symbolic representation

# find . -perm -g=r -type f -exec ls -l {} \;
Will display all files with group permission read. Not files with readonly group permission

# find . -perm g=r -type f -exec ls -l {} \;
Will dispay files with 040 permission. i.e files with group read only permisison

# find . -perm 040 -type f -exec ls -l {} \;
Will dispay files with 040 permission. i.e files with group read only permisison

Special permissions on files and directories in linux are : SetUID, SetGID and Sticky bit.

With the help of “chmod” command  we can implement the special permissions on file and directories.

SUID / Set User ID : A program is executed with the file owner’s permissions (rather than with the permissions of the user who executes it).

SGID / Set Group ID : Files created in the directory inherit its GID, i.e When a directory is shared between the users , and sgid is implemented on that shared directory , when these users creates  directory, then the created directory has the same gid or group owner of its parent directory.

Sticky Bit :  It is used mainly used on folders in order to avoid deletion of a folder and its content by other user though he/she is having write permissions. If Sticky bit is enabled on a folder, the folder is deleted by only owner of the folder and super user(root). This is a security measure to suppress deletion of critical folders where it is having full permissions by others.

SUID Example : passwd command
When normal user  try to change his/her  password  , passwd command is used ,  which is owned by root. This passwd command file will try to edit some system config files such as /etc/passwd, /etc/shadow etc. So passwd command is set with SUID to give root user permissions to normal user so that it can update /etc/shadow and other files.
Assign  suid to a File :

# chmod  u+s testfile.txt OR #  chmod 4750  testfile.txt

In this example , 4 indicates SUID bitset, 7 for full permissions for owner, 5 for write and execute permissions for group, and no permissions for others.

SGID Example :

# chmod g+s OR # chmod 2750 

Here in 2750, 2 indicates SGID bitset, 7 for full permissions for owner, 5 for write and execute permissions for group, and no permissions for others.

StickyBit Example : 

# chmod o+t /opt/ftp-data  or # chmod +t /opt/ftp-data OR # chmod 1757 /opt/ftp-dta

In this example , 1 indicates Sticky Bit set, 7 for full permissions for owner, 5 for read and execute permissions for group, and ful permissions for others.

Note : To check the special permissions , use these commands :

# ls   -l  

# ls -ld  

courtesy:http://foralllinux.blogspot.com