1. Red Hat Linux 5 - basic instructions ①

User Identification confirmation

whoami - to confirm login account

su - It means 'substitue user'. It's used to change another user ID, not to login,to use another new shell. Commonly it's used to change root account for a moment to do management work. then return to the previous login account.

passwd <ID>- used to change password.

File, Directory

ls [directory] [option]- Show Files and directories list.
  -l : Show specific info of files.
  -a : Show all files,regardless of the type of files.

mv <original filename> <new filename>: move or rename files.

chmod( permission ) <permission option> <objective file>
  d rwx rwx rwx : The first character is either directory or file. 'd' means directory, '-'
                           means file. The first "rwx" is the authority of an owner. The second one 
                           is the authority of a group. The final one is the authority of other users.
   To give an authority 
      1) rwx(421) add the number. - give owner, all groups, all users an authority.
              read + write + execution 7, read + write 6,
              read + execution 5,  read 4, write + execution 3, write 2, execution 1
      2) a( all ), u( user ), g( groups ), o( other ) / r( read ), w( write ), x( execution )
          + ( add permission ), - ( remove permission )
        ex ) chmod 777 redhat -> Give all owners, groups, users all authorities.
               chmod u+x redhat -> Give owner execution autority.

Link

ln -s <object of link> <filename of link> : object can be file or directory.
  ex ) ln -s a b : Make b link to point at a file or directory.
         cd b : Enter a which a point at