Study of linux commands
Aim:-
Study of Linux commands
*********************************************
Theory:-
Introduction to
Linux
Linux is a completely free reimplementation of the POSIX specification,
with SYSV and BSD extensions (which means it looks like Unix, but does not come
from the same source code base), which is available in both source code and
binary form. Its copyright is owned by Linus Torvalds and other contributors,
and is freely redistributable under the terms of the GNU General Public License
(GPL). A copy of the GPL is included with the Linux source. Linux, per
se, is only the kernel of the operating system, the part that controls
hardware, manages files, separates processes, and so forth. There are several
combinations of Linux with sets of utilities and applications to form a
complete operating system. Each of these combinations is called a distribution
of Linux. The word Linux, though it in its strictest form refers
specifically to the kernel, is also widely and correctly to refer to an entire
operating system built around the Linux kernel. Linux is not public
domain, nor is it `shareware'. It is `free' software, commonly called freeware
or Open Source Software and you may give away or sell copies, but you
must include the source code or make it available in the same way as any
binaries you give or sell. If you distribute any modifications, you are legally
bound to distribute the source for those modifications.
Linux Flavors –
Debian
Ubuntu
Fedora
OpenSUSE
Mandriva
Slackware
FreeBSD
Mint
PCLinuxOS
What is Ubuntu?
Ubuntu is a community
developed operating system that is perfect for laptops, desktops and servers. Whether you use it at home, at
school or at work Ubuntu contains all the applications you'll ever need, from
word processing and email applications, to web server software and programming
tools. Ubuntu is and always will be free of charge. You do not pay any
licensing fees. You can download, use and share Ubuntu with your friends,
family, school or business for absolutely nothing. We issue a new desktop and server release every six months. That means you'll always
have the latest and greatest applications that the open source world has to
offer. Ubuntu is designed with security in mind. You get free security
updates for at least 18 months on the desktop and server. With the Long
Term Support (LTS) version you get three years support on the desktop, and five
years on the server. There is no extra fee for the LTS version, we make our
very best work available to everyone on the same free terms. Upgrades to new
versions of Ubuntu are and always will be free of charge.
Features –
Open Office - A complete
productivity suite
Integrated email and
calendaring
Easy note-taking with
Tomboy
Safe, easy and tabbed web
browsing
Easy editing and uploading
of photos
Music and videos
Linux Commands –
·
mkdir - make
directories
Usage mkdir
[OPTION] DIRECTORY , Options Create the
DIRECTORY(ies), if they do not already exist. Mandatory arguments to long
options are mandatory for short options too.
-m,
mode=MODE set permission mode (as in chmod), not rwxrwxrwx - umask
-p,
parents no error if existing, make parent directories as needed
-v,
verbose print a message for each created directory
-help
display this help and exit
-version
output version information and exit
·
cd - change
directories
Use
cd to change directories. Type cd followed by the name of a directory to access
that directory.Keep in mind that you are always in a directory and can navigate
to directories hierarchically above or below.
·
mv- change the
name of a directory
Type
mv followed by the current name of a directory and the new name of the
directory.
Ex:
mv testdir newnamedir
·
pwd - print
working directory
will
show you the full path to the directory you are currently in. This is very
handy to use, especially when performing some of the other commands on this
page
·
rmdir
- Remove an existing directory
·
rm –r - Removes directories and files within the
directories recursively.
·
chown - change
file owner and group , Usage chown
[OPTION] OWNER[:[GROUP]] FILE ,
chown [OPTION] :GROUP FILE ,chown
[OPTION] --reference=RFILE FILE
Options
Change the owner and/or group of each FILE
to OWNER and/or GROUP. With --reference, change the owner and group of
each FILE to those of RFILE.
-c,
changes like verbose but report only when a change is made
-dereference
affect the referent of each symbolic link, rather than the symbolic link itself
-h,
no-dereference affect each symbolic link instead of any referenced file (useful
only on systems that
can change the ownership of a
symlink)
-from=CURRENT_OWNER:CURRENT_GROUP
change the owner and/or group of each file only if its current owner and/or
group match those specified here. Either may be omitted,
in which case a match is not required for the omitted attribute.
-no-preserve-root
do not treat `/' specially (the default)
-preserve-root
fail to operate recursively on `/'
-reference=RFILE
use RFILE's owner and group rather than the specifying OWNER:GROUP values
-R,
-recursive operate on files and directories recursively
-v,
-verbose output a diagnostic for every file processed
The
following options modify how a hierarchy is traversed when the -R option is
also specified. If more than one is specified, only the final one
takes effect.
-H
if a command line argument is a symbolic link to a
directory, traverse it
-L
traverse every symbolic link to a directory encountered
-P
do not traverse any symbolic links (default)
·
chmod - change
file access permissions - Usage chmod
[-r] permissions filenames
r
Change the permission on files that are in the subdirectories of the directory
that you are currently in.
permission Specifies the rights that are being granted. Below is the
different rights that you can grant in an alpha numeric
format.filenames File or directory that you are associating the rights
with Permissions
u
- User who owns the file.
g
- Group that owns the file.
-
Other.
a
- All.
r
- Read the file.
w
- Write or edit the file.
x
- Execute or run the file as a program.
Numeric
Permissions:
CHMOD
can also to attributed by using Numeric Permissions:
400
read by owner
040
read by group
004
read by anybody (other)
200
write by owner
020
write by group
002
write by anybody
100
execute by owner
010
execute by group
001
execute by anybody
·
ls - Short
listing of directory contents
-a
list hidden files
-d
list the name of the current directory
-F
show directories with a trailing '/' executable
files with a trailing '*'
-g
show group ownership of file in long listing
-i
print the inode number of each file
-l
long listing giving details about files and directories
-R
list all subdirectories encountered
-t
sort by time modified instead of name
·
cp - Copy
files
cp
myfile yourfile - Copy the files "myfile" to the file
"yourfile" in the current working directory. This command will create
the file "yourfile" if it doesn't exist. It will normally overwrite
it without warning if it exists.
cp
-i myfile yourfile –
With
the "-i" option, if the file "yourfile" exists, you will be
prompted before it is overwritten.
cp
-i /data/myfile
Copy
the file "/data/myfile" to the current working directory and name it
"myfile".
Prompt
before overwriting the file.
cp
-dpr srcdir destdir
Copy
all files from the directory "srcdir" to the directory
"destdir" preserving links (-poption), file attributes (-p option),
and copy recursively (-r option). With these options, a directory and all it
contents can be copied to another dir
·
ln - Creates a
symbolic link to a file.
ln
-s test symlink - Creates a symbolic link named symlink that points to the file
test Typing "ls -i test symlink" will show the two files are
different with different inodes. Typing "ls -l test symlink" will
show that symlink points to the file test.
·
locate - A fast database driven file locator.
·
slocate -u
This
command builds the slocate database. It will take several minutes to complete
this command.This command must be used before searching for files, however
cron runs this command periodically on most systems.locate whereis
Lists all files whose names contain the string "whereis". directory.
·
more - Allows file contents or piped output to be sent to the
screen one page at a time
·
less - Opposite of the more command
·
cat - Sends file contents to standard output.
This is a way to list the contents of short files to the screen. It works
well with piping.
·
whereis - Report all known instances of a command
·
wc - Print byte, word, and line counts
·
bg - bg jobs Places the current job (or, by using the
alternative form, the specified jobs) in the background, suspending its
execution so that a new user prompt appears immediately. Use
the jobs command to discover the identities of background jobs.
·
cal month year - Prints a calendar for the specified month
of the specified year.
·
cat files - Prints the contents of the specified
files.
·
clear - Clears the terminal screen.
·
cmp file1
file2 - Compares two files,
reporting all discrepancies. Similar to the diff command, though the
output format differs.
·
diff file1
file2 - Compares two files,
reporting all discrepancies. Similar to the cmp command, though the
output format differs.
·
dmesg - Prints the messages resulting from the most recent
system boot.
·
Fg - fg jobs - Brings the current job (or the
specified jobs) to the foreground.
·
file
files - Determines and
prints a description of the type of each specified file.
·
find path
-name pattern -print
Searches
the specified path for files with names matching the specified pattern (usually
enclosed in single quotes) and prints their names. The find command
has many other arguments and functions; see the online documentation.
·
finger users
- Prints descriptions of the
specified users.
·
free
- Displays the amount of used
and free system memory.
·
ftp hostname
Opens
an FTP connection to the specified host, allowing files to be transferred. The
FTP program provides subcommands for accomplishing file transfers; see the
online documentation.
·
head
files - Prints the first
several lines of each specified file.
·
ispell
files - Checks the spelling
of the contents of the specified files.
·
kill
process_ids
kill
- signal process_ids
kill
-l
Kills
the specified processes, sends the specified processes the specified signal
(given as a number or name), or prints a list of available signals.
·
killall
program
killall
- signal program
Kills
all processes that are instances of the specified program or sends the
specified signal to all processes that are instances of the specified program.
·
man title - man section title - Prints the specified man
page.
·
ping host - Sends an echo request via TCP/IP to the
specified host. A response confirms that the host is operational.
·
reboot - Reboots the system
(requires root privileges).
·
shutdown minutes
shutdown
-r minutes
Shuts
down the system after the specified number of minutes elapses
(requires root privileges). The -r option causes the system to be
rebooted once it has shut down.
·
sleep
time - Causes the command
interpreter to pause for the specified number of seconds.
·
sort
files - Sorts the specified
files. The command has many useful arguments; see the online documentation.
·
split
file - Splits a file into
several smaller files. The command has many arguments; see the online
documentation
·
sync - Completes all pending input/output operations (requires root privileges).
·
telnet host - Opens a login session on the specified
host.
·
top - Prints a display of system processes that's continually
updated until the user presses the q key.
·
traceroute
host - Uses echo requests
to determine and print a network path
to the host.
·
uptime - Prints the system uptime. w - Prints
the current system users.
·
wall - Prints a message to each user except those
who've disabled message reception. Type Ctrl-D to end the
message.
Conclusion:- Hence study of linux
commands is completed successfully.
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