Given below are some typical commands used in bash environment under a variety of circumstances. Check out the listing and I am sure everyone who reads this will be benefited from at least one of the following…
 du utility command
You can use the du utility to estimate file space usage. For example,
user@GNULinux:~$ du -sh /home/user/photorec.ses
-s for summarizing and -h for making the displayed size human readable. Look at another example,
user@GNULinux:~$ cd /home/
user@GNULinux:/home$ du -sh *
 Freeze a process temporarily using ID
For a GNU/Linux user explanation about the kill command is totally unnecessary. But the kill command is misleading. Only some indications of the kill command actually terminate the target process. kill -STOP suspends the target process and can be resumed by kill -CONT. This particular option can be useful in order to conduct some investigation on the occurence of some doubtful process running on the system. Know the process ID by top command.
user@GNULinux:/home$ kill -STOP 2255 freezes process 2255 and
user@GNULinux:/home$ kill -CONT 2255 resumes it.
 join command
join command combines lines from two files based on a common field. In the example below we have two files. One containing the first name and second containing the last name. Both the files contain the same index.
user@GNULinux:~$ cat 1
user@GNULinux:~$ cat 2
user@GNULinux:~$ join 1 2
100 Tom John
101 Alen Justin
102 Kevin Paul
 stat for displaying status/properties
stat command can be used either to check the status/properties of a single file or the file system.
user@GNULinux:~$ stat /etc/fstab
Size: 996 Blocks: 8 IO Block: 4096 regular file
Device: 809h/2057d Inode: 2359298 Links: 1
Access: (0644/-rw-r–r–) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2013-06-26 18:28:25.533022860 +0530
Modify: 2013-06-24 18:15:10.303597639 +0530
Change: 2013-06-24 18:15:10.303597639 +0530
Display the status of the file system using option –f
user@GNULinux:~$ stat -f /
ID: 2c64964204156b69 Namelen: 255 Type: ext2/ext3
Block size: 4096 Fundamental block size: 4096
Blocks: Total: 12302800 Free: 10766735 Available: 10141775
Inodes: Total: 3129344 Free: 2924549
 List the open files
lsof command stands for ls open files, which will list all the open files in the system. Simply executing lsof may return lot of records as output which may not be useful. lsof used with wc gives you the count of open files.
user@GNULinux:~$ lsof | wc -l
Use lsof –u option to display all the files opened by a specific user.
user@GNULinux:~$ lsof -u user
If you like to view all the users who are using a particular file, use lsof as shown below
user@GNULinux:~$ lsof /bin/nano
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
nano 3568 user txt REG 8,9 191960 2883673 /bin/nano