CS155: NFS, Permissions, and pico Lecture 4

1
CS155 NFS, Permissions, and picoLecture 4
2
Review

• Commands wc, grep, cut, sort, uniq
• Examples
• cut -f2 -d names sort -n
• Selects the second space delimited column from
  names and sorts the lines numerically
• grep ID .txt
• Searches for lines containing ID in files
  that end with .txt
• sort ids uniq wc l
• Sort the ids file, remove duplicate lines, and
  count

3
NFS More File System Facts
4
Permissions, Ownership, and ls -l
gt ls l total 8 -r-xr-xr-x 1 smith under 235
Dec 18 1222 program1 -rw------- 1 boese fac
4 Jan 19 1443 my_file2 drwx------ 2 boese
fac 4096 Jan 19 1444 new_dir
Owner
Group
Permissions

• Every file and directory in the file system is
  owned by some user and belongs in some group.
• Generally, a file is owned by whoever created it
  and belongs to that users default group.

5
Permissions in Detail

• d in the first position means directory
• - in the first position means file
• r read
• w write
• x execute
• The permissions can be different for user, group
  and other (everyone else)

6
Permissions What do they mean?

• r gives permission to view the contents of a
  file or directory
• w gives you permission to modify a file or
  directory
• x gives you permission to execute a file or
  cd into a directory
• Programs must have the execute permission set in
  order to be run.

7
Permissions Examples

• drwxr-x---
• owner list, modify (add or rm files), and cd
• group list and cd
• other no access
• -r--r--r-- a file that can only be read
• -rw-rw-r-- a file that can be read by everyone
  but only written to by the owner and group members

8
chmod Changing Permisions

• chmod change mode
• Often we will want to grant or restrict access to
  certain files or directories. chmod allows us to
  do this in two ways.
• We can add or subtract permissions for user u ,
  group g , and other o
• We can also set all permissions at once.

9
chmod use

• chmod MODE,MODE file
• MODE is formed by combining
• level u , g , or o (or a combination),
• modify symbol , - , or
• permission r , w , x
• Example chmod ugwx gives user and group write
  and execute permissions

10
chmod examples

• chmod ugor file give everyone permission only
  to read file. (-r--r--r--)
• chmod goxw file grant group and other execute
  and write access to file. (-r--rwxrwx)
• chmod o-rwx file take away read, write, and
  execute access from users not in group or user.
• (-r--rwx---)
• chmod urwx file give the user read, write, and
  execute access. (-rwxrwx---)

11
chmod by numbers

• chmod file
• is a three digit number specifying the access
  for user, group, and other.
• Example chmod 754 file will give user rwx, group
  r-x, and other r--.

0 --- 4 r-- 1 --x 5 r-x 2 -w- 6
rw- 3 -wx 7 rwx
12
Text Editors

• A text editor allows you to modify the contents
  of a file in a convenient way.
• For Windows users, think notepad not Microsoft
  Word.
• We will cover three pico, emacs, vim
• Pico is the simplest (and least powerful). We
  will cover it first.

13
PICO

• A simple text editor that provides basic editing
  functions
• Most commands are performed by pressing Ctrl and
  some other key.
• The symbol in front of a character means press
  Ctrl and that character.

14
pico Some Commands

• Up Ctrl-P
• Down Ctrl-N
• Left Ctrl-B
• Right Ctrl-F
• Beginning of Line Ctrl-A
• End of Line Ctrl-E
• Page Up Ctrl-Y
• Page Down Ctrl-V
• Cut Text Ctrl-K
• Paste Text Ctrl-U
• Save Ctrl-O
• Quit Ctrl-X