Transcript tutorial-2-119279288148975-5 - Home

Linux Overview
Outline
• Linux file system (FS)
– Useful commands for manipulating the FS
• Linux vs. Windows
• What did you learn from Assignment #1
– sudo
– Apt-get
– Pipes
– Command prompt
Linux Filesystem
Everything is a File
Linux Filesystem
• Filesystem is a method for storing and
organizing computer files and the data they
contain to make it easy to find and access.
• Different operating systems normally use
different file systems.
Linux Filesystem
• The filesystem in Linux stores
– the kernel
– the executable commands supported by the OS
– configuration information
– user data
– and special files that are used to give controlled
access to system hardware and OS functions.
Linux Filesystem
• Items stored in the filesystem are of four types:
– Ordinary files contain text, data, or program
information. Files can not contain other files or
directories.
– Directories containers that hold files, and other
directories.
– Devices are used in the same way as ordinary files
providing applications with easy access to the
hardware devices.
– Links which is a pointer to another file
Linux Filesystem
• The system is laid out as a hierarchical tree
structure. The top-level directory is the 'root'
designated by a slash '/'.
• Each directory can have many child
directories, but only one parent directory.
Linux Filesystem
Linux Filesystem
• The path to a certain location can be specified
as:
– Absolute path from root
e.g.
/root/home/will
– Relative path
e.g.
Accessing play from user “zeb”
../will/play
Root Common Subdirectories
Common Subdirectories
Directory Stands for
Content
/
root
Top-level directory in the hierarchical tree
/bin
Binaries
Contains binaries used by both the system administrator and
non-privileged user e.g. command ‘ls’ is stored here
/dev
Devices
Contains hardware devices directories. It is a virtual directory
/etc
Et cetra
Contains configuration files for running applications
/home
Contains user subdirectories
/lib
Libraries
/mnt
Mount
/proc
Processes
/root
Contains shared libraries e.g. C, Perl, Python general libraries
Contains information about the system e.g. process that are
running. It is a virtual directory
Default home directory for the system administrator. Isolated
to increase security
Common Subdirectories
Directory
Stands for
Content
/sbin
Secure
Binaries
/tmp
Temporaries Contains temporary files
/usr
Unix System
Resources
Contains subdirectories such as /usr/doc which contains
system documentations, /usr/local the local hosts directory
/var
Variables
Contains log and spool files
/boot
Contains secured binaries that are only accessed by
privileged users e.g. fdisk, partitioning tool is kept here
Contains Linux kernel
Useful Commands
CD
• $ cd path
– changes your current working directory to path (which can
be an absolute or a relative path). One of the most
common relative paths to use is '..' (i.e. the parent
directory of the current directory).
• $ cd 
– resets your current working directory to your home
directory (useful if you get lost).
• $ cd - 
– If you change into a directory and you subsequently want
to return to your original directory, use
pwd
• pwd - Displays the current directory ("working
directory").
• pwd displays the full absolute path to your
current location in the filesystem.
• $ pwd 
/usr/bin
• implies that /usr/bin is the current working
directory.
Filesystem Comparison
Linux vs. Window
Filesystem Comparison
Linux Filesystem
Windows Filesystem
Hierarchal
Structure
Only a single hierarchal directory
structure. Everything starts from
the root directory and then
expanded to subdirectories. It also
has various partitions, but under
the root directory. They are
‘mounted’ under specific
directories
(Unified scheme)
Various partitions, with directories
under those partitions
(Volume based file hierarchy)
Detection
Partition will not be detected
unless it has been mounted.
All partitioned detected and
booted, then each assigned a drive
letter.
Crossover
Can read/write FAT16 , FAT32
Can not unless with third party
support
Hidden Files
Implement with a name that
starts with a dot.
Tracks it as a file attribute
Types
ext2, ext3
FAT12, FAT16, FAT32, and or NTFS
Filesystem Comparison
Linux Filesystem
Windows Filesystem
Case
Sensitivity
Case sensitive. File.txt is not
the same as file.txt
Not case sensitive
Confirmation
Messages
Non existent e.g. when
deleting, user will not be
promoted whether to continue
with the operation or not
User will be prompted with each
action
Search Path
Does not look into the current
directories. It looks at the PATH
environment variable.
To run program in current
directory:
./ program
Checks current directory first then
looks at the PATH environment
variable
Slashes
Uses a forward slash “/”
Uses a backward slash “\”
Switch
Indication
Switches are preceded by “-”
Switches are preceded by “\”
Default Directory
• The default working directory is your user
home directory.
– /home/ubuntu
User name
• /home is equivalent to My documents
Running Privileged Commands
• How to run privileged commands as a normal
user?
– Use sudo command
• Sudo is a program which can be used by
normal users to execute as super users or any
other users.
Running Privileged Commands
Example
Running the following statement
sudo –l
Then entering password will produce a listing
of command that the user may execute as well
as how and as who they maybe executed.
Beware of the dark side of root
•
•
•
root user privileges are only needed for very specific tasks
with security risks: mounting, creating device files,
loading drivers, starting networking,
changing file ownership, package upgrades...
Even if you have the root password, your regular account
should be sufficient for 99.9 % of your tasks
(unless you are a system administrator).
In assignments, it is acceptable to use root.
In real life, you may not even have access to this account,
or put your systems and data at risk if you do.
Using the root account
In case you really want to use root...
• If you have the root password:
su - (switch user)
• In modern distributions, the sudo command gives you
access to some root privileges with your own user
password.
Example: sudo mount /dev/hda4 /home
Live process activity
•
top - Displays most important processes, sorted by cpu
percentage
top - 15:44:33 up 1:11, 5 users, load average: 0.98, 0.61, 0.59
Tasks: 81 total, 5 running, 76 sleeping, 0 stopped, 0 zombie
Cpu(s): 92.7% us, 5.3% sy, 0.0% ni, 0.0% id, 1.7% wa, 0.3% hi, 0.0% si
Mem: 515344k total, 512384k used, 2960k free, 20464k buffers
Swap: 1044184k total,
0k used, 1044184k free, 277660k cached
•
•
PID USER
3809 jdoe
2769 root
3006 jdoe
3008 jdoe
3034 jdoe
3810 jdoe
PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
25 0 6256 3932 1312 R 93.8 0.8 0:21.49 bunzip2
16 0 157m 80m 90m R 2.7 16.0 5:21.01 X
15 0 30928 15m 27m S 0.3 3.0 0:22.40 kdeinit
16 0 5624 892 4468 S 0.3 0.2 0:06.59 autorun
15 0 26764 12m 24m S 0.3 2.5 0:12.68 kscd
16 0 2892 916 1620 R 0.3 0.2 0:00.06 top
You can change the sorting order by typing
M: Memory usage, P: %CPU, T: Time.
You can kill a task by typing k and the process id.
Updating and installing packages
• Debian-based distros use a software installer
called apt-get, which uses the Debian dpkg
system to retrieve, unpack, and install
software.
• Apt-get is the command you use to get that
software.
• Synaptic is the GUI for apt-get
Pipes
• Unix pipes are very useful to redirect the
•
standard output of a command to the standard
input of another one.
Examples
–cat *.log | grep -i error | sort
–grep -ri error . | grep -v “ignored” | sort -u \ >
serious_errors.log
• This one of the most powerful features in Unix
shells!
Command prompt
• User_name@device_name:~$
– ubuntu@ubuntu:~$
• Use UP arrow key to invoke previous
commands
• Use TAB to auto-complete commands
Conclusion
• You need to know the difference between
relative and absolute path when dealing with
Linux directories
• You need to know how Linux FS is different
from Windows FS
• You need to know when to switch to super
user privileges
References
• The basic similarities between Linux and DOS
– http://www.control-escape.com/linux/lxbasics.html
• Introduction to Unix
– http://wwwhomes.doc.ic.ac.uk/~wjk/UnixIntro/
• Windows-to-Linux Roadmap
– http://www.ibm.com/developerworks/linux/librar
y/l-roadmap1.html