Browsing the Filesystem on Linux

Linux File Hierarchy Concepts

• Files and Directories are organized into a single rooted inverted tree structure, including distinct physical volumes such as Floppy Disks, CD-ROMs and Multiple Hard Drives.
• Filesystem begins at the root directory, represented by lonely forward slash (/).
• Names in Linux File Hierarchy are case sensitive.
• Paths are delimited by / such as /usr/share/bin/X11/X
• Each shell and system process has a current working directory.
• . refers to the current working directory.
• .. refers to the parent directory of any particular directory - just one level up in the file hierarchy.
• Files and Directories whose name begin with a . are hidden.
• A user’s path is a list of directories that are searched for commands typed at the command line.

Some Important Directories

1. Home Directories: /root, /home/username
2. User Executables: /bin, /usr/bin, /usr/local/bin
3. System Executables: /sbin, /usr/sbin, /usr/local/sbin
4. Shared Libraries: /lib, /usr/lib, /usr/local/lib
5. Kernels & Boot-loaders: /boot
6. Configuration Files: /etc
7. Device Files: /dev
8. Temporary Files: /tmp
9. Other Mount-points: /media, /mnt
10. Server Data: /var, /srv
11. System Informations: /proc, /sys
12. Optional Applications: /opt

1. Home Directories

• Every user has a home directory.
• The root user’s home directory is /root.
• Most non-root user’s home directories are in /home/username.

2/3. User/System Executables

• The essential binaries reside in /bin for user and /sbin for systems.
• The non essential binaries, such as graphical environments or office tools installed in/usr/bin and /usr/sbin.
• The software compiled from the source code, usually go in /usr/local/bin and/usr/local/sbin.

4. Shared Libraries

• The lib directory contains the libraries that provide shared code used by many Linux Applications.

5. Kernels & Boot-loaders

• The boot loader is in charge of loading the core of the Linux, called kernel, into the memory.
• The boot loader, kernel and loader’s configuration files are stored in /boot.

6. Configuration Files

• Most of the configuration files are stored in /etc and its subdirectories.

7. Device Files

• Most of the device files are stored in /dev and its subdirectories.

8. Temporary Files

• The /tmp directory is usually used by many Linux Applications for storing temporary data.
• Once a day system automatically deletes any files over ten days old in /tmp.

9. Other Mount-points

• Filesystems of the removable media are usually mounted under /media.
• For Example: A cdrom is usually mounted under /media/cdrom.

10. Server Data

• The /var directory contains the regularly changing system files such as logs, print spools and email spools.
• The /srv directory contains the server data such as databases and web pages.

11. System Informations

• The /proc directory is a special dynamic directory that provides the informations about a running Linux system and allows some tweaking while a system is running.
• The /sys directory is related to the hardware.

12. Optional Applications

• The /opt directory provides a location for optional applications to be installed.

Files and Directory Names

• Names may be up to 255 characters.
• Names are case sensitive.
  • For Examples: MAIL, Mail, mail and maiL
  • Again, possible, but not be wise.
• All characters are valid, except forward-slash (/).
  • It maybe unwise to use certain special characters in files and directory names.
  • Among the characters to avoid are: <>?*” and quotation marks, as well as spaces, tabs, and other non-printable characters.
  • Some characters should be protected with quotes when referencing them.

ls -l "file name with spaces.txt"
-rw-rw-r--. 1 mitesh mitesh 0 Aug 12 18:44 file name with spaces.txt

NOTE!: Absent the quotes, you would be asking the system to list the four different files.

Absolute and Relative Pathnames

Absolute Pathnames

• Begin with a forward slash (/).
• Complete road map to the file location.
  • For Example: /usr/share/doc/HTML/index.html
• Can be used anytime you wish to specify a file name, Regardless of the current working directory.

Relative Pathnames

• Do not begin with a forward slash.
• Specify location relative to your current working directory.
• Can be used as a shorter way to specify the file name.

Current Working Directory

• Each shell and system process has a current working directory.
• The pwd command displays the absolute path of the shell’s current working directory.

[mitesh@Matrix ~]$ pwd
/home/mitesh

Changing Directories - cd command

• The cd command are used to change the directory.
• The only argument to the cd command is either an absolute or relative pathname, or a shortcut representing the directory to which you wish to change.

To absolute or relative path

cd /home/mitesh/Desktop
cd projects/docs

To your home directory

cd
cd ~

To a directory just one level up

cd ..

To your previous working directory

cd -

Listing Directory Contents - ls command

• List the contents of the current working directory or a specified directory.

ls [OPTION]... [FILE]...

ls;     ls -l;      ls -R
ls -a;  ls -l /usr;
ls /;   ls -ld /usr;

List the files and directories in the current working directory

[mitesh@Matrix ~]$ ls
work

List the hidden files and directories

[mitesh@Matrix ~]$ ls -a
.bash_history  .bash_logout  .bash_profile  work

List the files and directories of the specified directory

[mitesh@Matrix ~]$ ls /
bin   cgroup  etc   lib    lost+found  misc  net  proc  sbin     srv  tmp  var
boot  dev     home  lib64  media       mnt   opt  root  selinux  sys  usr

Long Listing

[mitesh@Matrix ~]$ ls -l /usr
total 148
dr-xr-xr-x.   2 root root 36864 Aug  8 21:51 bin
drwxr-xr-x.   2 root root  4096 Dec  4  2009 etc
drwxr-xr-x.   2 root root  4096 Dec  4  2009 games
...output truncated...

Display directory information, not their contents

[mitesh@Matrix ~]$ ls -ld /usr
drwxr-xr-x. 13 root root 4096 Aug  4 20:58 /usr

NOTES!: It has no effect when filenames are passed as arguments.

Recurse though directories

[mitesh@Matrix ~]$ ls -R

Copying Files and Directories - cp command

• The cp command is used to copy files and directories.

cp [OPTION]... SOURCE DEST
cp [OPTION]... SOURCE... DIRECTORY

Options

* -i(interactive): Ask before overwriting a file
* -r(recursive): Recursively copy an entire directory tree
* -p(preserve):         Preserve the permissions, ownership, and time stamps
* -a(archive):         Copy files and directories recursively (like -r) while preserving permissions (like -p)

The Destination

• If the destination is a directory, a copy of the source file is placed in that directory with the same name as the source.
• If the destination is a file, a copy of the source file is created with that destination name.

WARNING THE CP COMMAND ALWAYS OVERWRITES THE DESTINATIONS!!

[mitesh@Matrix ~]$ ls /home/mitesh/
testfile

[mitesh@Matrix ~]$ cp ~mitesh/testfile /tmp/
[mitesh@Matrix ~]$ ls /tmp/
testfile
... other output omitted...

[mitesh@Matrix ~]$ cp ~mitesh/testfile /tmp/mitesh_test_file
[mitesh@Matrix ~]$ ls /tmp/
mitesh_test_file
... other output omitted...

Moving and Renaming Files and Directories - mv command

• The mv command is used to move/rename files and directories.

mv [OPTION]... SOURCE DEST
mv [OPTION]... SOURCE... DIRECTORY

• Aside from a couple of switches, mv and cp function identically -- The only difference is that with cp source and destination both are presents and with mv source disappears only destination is there.
• Destination works like cp command.

[mitesh@Matrix ~]$ ls /home/mitesh/
testfile

[mitesh@Matrix ~]$ mv ~mitesh/testfile /tmp/
[mitesh@Matrix ~]$ ls ~mitesh
[mitesh@Matrix ~]$ ls /tmp/
testfile
... other output omitted...

[mitesh@Matrix ~]$ mv ~mitesh/testfile /tmp/mitesh_test_file
[mitesh@Matrix ~]$ ls ~mitesh
[mitesh@Matrix ~]$ ls /tmp/
mitesh_test_file
... other output omitted...

Creating and Removing Files and Directories

Touch command

• The touch command is used to creates empty files or update file timestamps

touch [OPTION]... FILE...

rm command

• The rm command is used to remove files.

rm [OPTION]... FILE...

Options

• -i(interactive): Prompt before every removal
• -f(forcefully): Forcefully removed without any prompt
• -r(recursive): Remove directories and their contents recursively

[mitesh@Matrix notes]$ ls
file1  file2  file3  file4  file5

[mitesh@Matrix notes]$ rm -i file1
rm: remove regular file `file1`? y
[mitesh@Matrix notes]$ ls
file2  file3  file4  file5

[mitesh@Matrix notes]$ rm -f file2
[mitesh@Matrix notes]$ ls
file3  file4  file5

[mitesh@Matrix ~]$ rm -ri notes/
rm: descend into directory `notes`? y
rm: remove regular empty file `notes/file1`? y
rm: remove regular empty file `notes/file2`? y
rm: remove directory `notes'? y

[mitesh@Matrix ~]$ rm -rf notes/

mkdir command

• The mkdir command is used to creates the directories.

mkdir [OPTION]... DIRECTORY...

Options

• -p(parents): Make parent directories as needed

[mitesh@Matrix ~]$ mkdir work
[mitesh@Matrix ~]$ ls
work

[mitesh@Matrix ~]$ mkdir -p work/labs
[mitesh@Matrix ~]$ ls
work
[mitesh@Matrix ~]$ ls work/
labs

rmdir command

• The rmdir command is used to remove empty directories.

rmdir [OPTION]... DIRECTORY...

NOTE!: The rmdir command removes only empty directories.
To remove a directories and its contents, use rm -r.

Using Nautilus

• Nautilus is a GNOME Graphical File System Browser.
• Nautilus can run in one of two modes:

1. Spatial Mode

• Spatial mode is designed for new users and the simplest in the terms of user interface clutter.
• Windows have a very basic layout with no toolbar and when a directory is double-clicked it opens in its own window.
• A menu in the lower-left of each window allows the user to list and select parent directories.

2. Browser Mode

• Browser Mode provides a more traditional file manager interface.
• Windows have a very advance layout with toolbar, menubar, and side panel and when a directory is double-clicked it opens in the same windo.
• Browser mode can be started by selecting Application -> System Tools -> File Browser

Nautilus can be accessed in a number of ways

• Desktop Icons
  • Home: Your home directory
  • Computer: Root filesystems, Network resources, and Removable media

Nautilus Shortcuts

• Ctrl+c Copy
• Ctrl+v Paste
• Ctrl+a Select All
• Ctrl+l Open Location dialog
• Ctrl+q Close all nautilus windows
• Ctrl+Shift+w Close all the parent windows
• Ctrl+Shift+n Creates new Directory

Moving and Copying in Nautilus

1. Drag-and-Drop
   • Drag: Move on same filesystem, copy on different filesystem
   • Drag+Ctrl: Always Copy
   • Drag+Alt: Ask whether to copy,move or creates symbolic link (alias)
2. Context Menu
   • Right-click to rename, cut, copy or paste

Determining File Content

• Check file type before opening it with file command.
• file command prints its best guess of the type of data contained in a file. (by using/usr/share/magic)
• Files can contains many types of data such as ASCII (Plain Text, HTML, Executable Shell Scripts, C Program Source Code, Mailbox-format Text) or Binary ( Compiled Executables, Compressed Data, Images and Sound Samples).