July 2, 2015

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).

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