Linux HowTo: Useful Shell Commands - 1

Here is a little compilation of useful shell commands. The first in the series. More posts will follow in the same vein..
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-Processes:

       # ps -ef                                         - every process and full output

       # ps -fu mrinal                              - full output of processes running as user mrinal

-Sessions:

 

        # id -un                                        - Currently logged in user

        # last mrinal                                - Last time user mrinal logged in

        # ls -A                                          - List All files but not . or ..
-Files:
         # find . -mmin -30                       - Find files modified in last 30 min; +30 = more than 30 min ago

         # find . -ls | sort -nrk7                 - Find and sort by size

         #tac afile                                     - outputs  afile in reverse order ( opposite of cat ).

         #od                                             - dump of a file ( default is octal dump, thats why od)

         # od -An file                                - A=marks the type of dump denoted by n. n can be o (octal), d (decimal), x (hex)

         #pr   afile                                    - format afile for print [ adds a default header - date time, filename and page number ]

         #nl   afile                                    - numbers the lines of afile in the output
         #ls -lu afile                                  - reports last access time of afile