Linux

1
Linux

• Files

2
Files and directories

• As in Windows directories are structures which
  contain
• Other directories
• Files

3
Root directory

• Base directory
• All others are contained within this directory
• Not to be confuse with /root
• This is the home directory of the root user

4
Typical directories

• /etc configuration
• /var files that change (vary) such as logs
• /home structure containing user home directories
• /bin executables
• /sbin root user executables
• /usr regular user files
• /tmp
• /root
• /boot
• /dev used to access hardware resources
• /lib system libraries

5
Shell

• Command line environment
• Like the Windows DOS command line
• Prompt displayed
• Enter a command and bit enter
• Result (if any) returned, and next prompt
  displayed
• Or.. Error message

6
Commands

• pwd
• print working directory
• cd
• change directory
• mkdir
• rmdir
• ls
• touch

7
cd

• cd name
• changes to the name directory
• uses relative and absolute names
• one dot refers to current directory
• two dots refers to parent directory
• forward slash ( / ) indicates a directory name
• no slash indicates a subdirectory in the current
  directory

8
ls

• lists the names of files in a directory
• ls l
• long listing

9
touch

• updates the time stamp of a file to that time
• creates a new file (0 bytes) if the file does not
  exist

10
cp

• copy
• cp file1 file2

11
rm

• remove
• rm file1
• no undelete
• file is not placed into a recycle bin as in
  Windows

12
mv

• move
• mv file1 file2
• can be used to rename a file
• move it to a file with a different name

13
file

• displays the type of file
• file myfilename
• can be used to determine if the file is an
  executable or a text file which can be
  displayed using cat, more or less

14
cat

• views the contents of a file
• will scroll off the screen
• use the (pipe) to the more command
• cat more
• displays a screen, then stops
• spacebar will bring up next screen
• enter key brings up next line
• ctrl-x will exit the cat command

15
zcat

• cats a compressed file to the screen

16
less

• displays a screen at a time
• use Q to exit
• pageUp and pageDown as well as arrow keys can
  navigate the file

17
more

• displays a screen at a time

18
Filenames

• Length can be 256 characters
• upper or lower case
• peridos, numbers, punctuation marks
• NO SLASHES!

19
File Properties

• ls test
• -rwxr-xr-x 1 cmalinow users 1839423 Apr 1 1512
  test
• permissions
• user, group, other
• user
• group
• timestamp
• size

20
File Properties

• ls test
• -rwxr-xr-x 1 cmalinow users 1839423 Apr 1 1512
  test
• first character indicates type
• - regular file
• d directory
• user permission rwx
• group permission
• other permission

21
Changing owner

• chown username.groupname filename
• chown cmalinow.faculty testfileA
• command is invoked by root

22
chmod

• Changes permissions assigned to the file or
  directory
• used by root
• uses g, u, or o for group, user and other
• chmod ow test
• allows other to write to file
• chmod grw test
• allows the group to read and write

23
chmod

• read, write and execute assigned
• 4, 2, 1 respectively
• chmod 640 test
• user has 6 4 and 2 (read and write)
• group has 4 (read)
• others have 0 no access

24
File permissions

• When creating a file, permission are assigned
• umask determines the permissions to assign
• umask 022
• same pattern as permission in chmod
• umask executed as part of logging in

25
Whats a sticky bit?

• Dilemma
• depending on permissions set, any user in the
  group might be able to delete a file of another
  group member
• setting the sticky bit on a directory only allows
  the owner, the directory owner, or root to rename
  or delete the file
• set the sticky bit by chmod 1nnn
• 1 indicates to put a sticky bit on the directory
• chmod 1777 mydir
• ls ld mydir
• drwxrwxrwxt 2 cmalinow faculty etc
• t indicates the sticky bit is on