The File System

1
The File System

• Chapter 6 in your Textbook

2
Files in UNIX

• No restriction on type of information stored in
  them
• Everything is a file in UNIX
• Extensions are not enforced (.exe, .doc, etc)
  they are just a convenience
• Use file or type commands for this

3
Everything is a file

• Ordinary (regular) files
• Stream of characters (data, source code,
  executable, commands)
• Directory files
• Contain names and inode numbers of the files in
  the directory
• Device files
• Filenames are associated with physical devices

4
Filenames

• Up to 255 characters long
• Valid characters are
• Numbers and letters
• Period (.)
• Hyphen (-)
• Underscore (_)
• Avoid control characters

5
pwd commandknowing your current directory
/ (root)
home

• pwd
• /home/joe

joe
6
Creating directories and filesmkdir and touch
/ (root)
home
1

• pwd
• /home/joe

joe
2
dir
file
mkdir dir
3
touch file
7
Removing files withrm
/ (root)
home
joe
dir
4
rm file
8
cd to directories and coming HOME (without
arguments)
/ (root)
5

• pwd
• /home/joe
• cd dir

home
joe
6
pwd /home/joe/dir
dir
7
cd pwd /home/joe
9
Absolute pathname

• Uses the root (/) directory as reference
• Independent of current directory
• Note that this path always starts with /

10
Absolute pathname
/ (root)
1

• cd /home/joe
• pwd
• /home/joe

home
joe
2
cd /home/joe/dir pwd /home/joe/dir
dir
11
Relative pathname

• Uses the current directory (pwd) as reference
  point
• . (single dot)- references current directory
• ..(two dots) - references parent directory
• dir-name references a child directory by the
  name dir-name

12
Relative pathname
/ (root)
1
home
pwd /home/joe
2
joe
cd ./dir pwd /home/joe/dir
dir
cd .. pwd /home/joe
3
13
mkdir command

• Can take one or more arguments
• mkdir sales
• mkdir docs pay
• Use the -p option if progs doesnt already exist
• mkdir -p progs/java

joe
sales
dir
progs
pay
docs
java
14
rmdir command

• Removes existing empty directories
• rmdir sales pay
• Use rm -r option if not empty (be careful!)
• rm -r progs

joe
docs
dir
15
mv command

• Renaming one file
• mv f1 f2
• Moving one file to a directory
• mv f1 dir
• Careful, you can rename f1 to dir
• Moving more than one file to a directory
• mv f1 f2 f3 f4 dir
• dir must be an existing directory

16
df vs. du

• df outputs the total disks usage (Sys Admin)
• du is a command to output users individual disk
  consumption (in blocks)
• du .
• 320 ./cgi-bin
• 160 ./cs3375/img
• 1376 ./cs3375
• 464 ./cs1315

17
Compression utilities