Unix History
In
the 1960s, Massachusetts Institute of Technology, AT&T Bell Labs, and
General Electric developed an experimental operating system called Multics
(Multiplexed Information and Computing Service)for the GE-645 mainframe.
Multics
was highly innovative, but had many problems.
Bell
Labs, frustrated by the size and complexity of Multics but not the aims, slowly
pulled out of the project.
Summer
1969 Unix was developed.
UNIX is
much better, but much much expensive. Only for minicomputer for commercial
applications
People was
looking for a UNIX based system, which is cheaper and can run on PC
Both DOS, MAC
and UNIX are proprietary, i.e., the source code of their
kernel is protected
No modification is possible without paying high
license fees
Beginning of Linux
A famous professor Andrew Tanenbaum developed Minix, a simplified version of UNIX that runs on PC
Minix is for class teaching only. No intention
for commercial use
In Sept 1991, Linus
Torvalds, a second year student of Computer Science at the University of
Helsinki, developed the preliminary kernel of Linux, known as Linux version
0.0.1
It was put to the Internet and received enormous
response from worldwide software developers
By December came version 0.10. Still Linux was
little more than in skeletal form.
Message from
Professor Andrew Tanenbaum
" I
still maintain the point that designing a monolithic kernel in 1991 is a
fundamental error. Be thankful you are not mystudent. You would not
get a high grade for such a design :-)"(Andrew Tanenbaum to Linus
Torvalds)
"Linux is obsolete".
(Remark made by Andrew Tanenbaum)
But work went
on. Soon more than a hundred people joined the Linux camp. Then thousands. Then
hundreds of thousands
It was licensed under GNU General Public
License, thus ensuring that the source codes will be
free for all to copy, study and to change
Linux Today
Linux has been
used for many computing platforms PC, PDA, Supercomputer,…
Current kernel
version 2.6.13
Not only character user
interface but graphical user interface.
Advantages over Windows
It's
almost free to relatively inexpensive.
Source code is
included.
Bugs are fixed
quickly and help is readily available through the vast support in Internet.
Linux is more
stable than Windows.
Linux is truly
multi-user and multi-tasking.
multiuser: OS
that can simultaneously serve a number of users
multitasking: OS
that can simultaneously execute a number of programs
Linux is
mainly used in commercial applications, server
implementation.
More than 75%
current network servers are developed based on Linux or Unix systems. Due to
the relatively high reliability
Common
Distributions
Slackware RedHat
Caldera Mandrake Debian Corel
SuSe
1 ls - list
directory contents
SYNOPSIS
ls [OPTION]...
[FILE]
-a,
--all
do not ignore entries starting with . (display all file including hidden
files
-d,
--directory
list directory entries instead of
contents
-i,
--inode
print the index number of each file
-l use a long listing format
-r, --reverse
reverse order while sorting
-R, --recursive
list subdirectories recursively
-S sort by file size
Z, --context
Display security context so it fits on most
displays. Displays only mode, user,
group,
security context and file name.
ls -a [a-d] all
files between a to d
ls -a[!a-d] not list files between a to d
2 cat -
concatenate files and print on the standard output
cat [OPTION]...
[FILE]...
-A, --show-all
-n,
--number number all output lines
-T, --show-tabs display TAB characters as ^I
-E,
--show-ends display $ at end of each
line display
cat file name
display content of file
cat > file name
create new file
cat >>
file name append the content of
file
3 # pwd
Present working directory
Displays the location where the user is currently working
pwd [OPTION]...
4 # mkdir
to create a directory
syn: # mkdir <dir_name>
eg: # mkdir jai
syn: # mkdir -p <path_of_the_dir>
eg: # mkdir -p /ims/solaris/delhi
It creates the parent directory /ims/solaris along with the
directory delhi.
5 man - format and
display the on-line manual pages
man command
# man date
6 cd change directories
cd directories name
cd
.. change to parent directory
cd ~ change to user home directory
cd change to user home directory
7 who - show who
is logged on
-a, --all
same as -b -d --login -p -r -t -T -u
-b, --boot time
of last system boot
\
-l,
--login print system login
processes
8 whoami - print
effective userid
9 w - Show who is
logged on and what they are doing.
/var/run/utmp
information about who is currently logged on
10 rm - to remove the file
# rm <file-name>
# rm rose/Documents
to remove or to delete the file named rose
# rmdir - to remove or delete the directory
# rmdir <dir-nam/Documentse>
# rmdir delhi
will remove the directory name delhi only if it is empty
# rm -rf <dir-name>
# rm -rf delhi
will remove the contents of the directory named delhi and
delete the directory delhi.
where
-r = recurrsive
-f = forcefully
-i = interactive
11 type
find the location of command
type command
12 file - determine file type
file file name
13 wc - print newline, word, and byte counts for each
file
wc [OPTION]... [FILE]...
-c, --bytes print the byte counts
-l, --lines print the newline counts
-w, --words print the word counts
14 # cp - to copy a file or a directory
syn: # cp
<source_file> <destination_file>
eg: # cp rose jack
here the contents of the file named rose is copied to new
file named jack in the same location
# cp rose /Desktop/jack
will copy the contents of the file named rose to the
location /Desktop with the file name as jack
# cp rose /Desktop/
will copy the contents of the file named rose to the
location /Desktop with the same file name.
# cp -r <source_dir> <destination>
where
-r = recurrsive
To copy all the files and sub-directories inside a directory
15 diff [OPTION]... FILES
16 touch - change file timestamps
touch [OPTION]... FILE...
-a change only the access time
-m change only the
modification time
-t STAMP use
YYMMDDhhmm instead of current time
touch -t 3312131212
restoresymtable
17 more More is a filter for paging through
text one screenful at a time
# more
<file_name>
# more /etc/passwd
to view the contents of the file in pagewise
18 less Less is a program similar to more (1), but
which allows backward movement in the
file as well as forward movement
# less <file-name>
# less /etc/passwd
to view the contents of the file in pagewise
19 head Print
the first 10 lines of each FILE to standard output
# head -n <file-name>
# head -4 /etc/passwd
to view the first 4 lines of the specified file
20 tail Print
the last 10
lines of each FILE to standard output
# tail -n <file-name>
# tail -5 /etc/passwd
to view the last 5 lines of the specified file
21 # mv - to
rename or move or to cut and paste the file or directory
# mv jack rock
will rename the file jack as rock in the current location
# mv jack /Desktop/rock
will move the file jack to the location /Desktop with the
file name as rock.
NOTE: Source file "jack" will not be present
after moving
22 cut - remove sections from each line of files
cut OPTION... [FILE]..
23 tty - print the file name of the terminal connected to
standard input
24 init - Upstart
process management daemon
init 0 halt
init 6 reboot
25 sort - sort
lines of text files
sort [OPTION]... [FILE]
-r, --reverse reverse the result
of comparisons
-n, --numeric-sort compare
according to string numerical value
26 grep - print lines matching a pattern
grep - to search a
key word
# ls | grep rose
this command will look for the dir or file named rose
under the current location and display the
same if it is present in the present working directory
# grep <keyword> <file-name>
# grep one rose
will search for the keyword 'one' in the file named rose
and will display the same
# grep -i one rose
will search for the keyword 'one' by ignoring the case
and will display the same
# grep -v one rose
will dispaly all the lines and words expect 'one' from
the file rose.
# grep -h good rose jai
will look for the word 'good' in miltiple files named
rose and jai respectively.
To search a particular word from the file and to display
the name of the file having the search
keyword
-n,
--line-number Prefix each line of
output with the 1-based line number within
its input file.
grep test$ file name
display all line start with test
grep ^test file name display all line end with test
27 bc - An arbitrary precision calculator
language
28 date - print or set the system date and time
date [OPTION]... [+FORMAT]
date 121212302010 [mmddhhmmyyyy]
29 env - run a program in a modified environment
30 arch - print machine hardware name (same as uname -m)
arch
[OPTION].
31 find - search
for files in a directory hierarchy
find / -name passwd
find / -inum 1471670
32 locate - find
files by name
locate [OPTION]... PATTERN...
33 wall -- send a message to everybody’s terminal.
wall [-n] [ message ]
-n Suppresses the
normal banner printed by wall
34 write - send a message to another user
write user [ttyname]
35 ps - report a snapshot of the current
processes.
ps [options]
ps ax
ps axu
36 kill -
terminate a process
kill [-s signal|-p] [--] pid.
37 pgrep
- look up or
signal processes based on name and other
attributes
38 pkill terminate process by name
pkill [-s signal|-p] [--] process name
pkill -9 bash
39 cmp - compare two files byte by byte
cmp [OPTION]... FILE1 [FILE2
40 diff - compare files line by line
diff [OPTION]... FILES
41 uniq - report
or omit repeated lines
SYNOPSIS
uniq
[OPTION] filename
d,
--repeated only print
duplicate lines
-u,
--unique only print
unique lines
-i,
--ignore-case ignore differences in
case when comparing
42 echo - display a line of text
echo $PATH
echo $? 0
no error 1 error
43 export PATH=$PATH:/rr add last of path
export PATH=/yy:$PATH add start of path
44 gzip Gzip
reduces the size
of the named
files using Lempel-Ziv coding
(LZ77). Whenever possible, each file is
replaced by one
with the
extension .gz,
while keeping the same ownership modes, access and modi-
fication times.
# gzip <file-name>
# gzip passwd2
to zip the file the
file extension is .gz
45 gunzip can currently decompress files
created by gzip
# gunzip <file-name>.gz
# gunzip passwd2.gz
to unzip the file
46 bzip2 expects a
list of file names to accompany the command-line flags.
Each file is replaced by a compressed version of
itself, with the name
"original_name.bz2"
# bzip2 <file-name>
# bzip2 passwd3
to zip the file
file extension is .bz2
# bunzip2 <file-name>.bz2
to unzip the file
# tar - Tape ARchieve
# tar -cvf <file-name>.tar <source-file>
# tar -cvf one.tar passwd6
here
-c = to create the archieve
-v = verbose (detail) mode
-f = forcefully
here a tar file named one.tar is created from the source
file
passwd6
# tar xvf <file-name>.tar
# tar xvf one.tar
will extract the file to the current location
here
-x = to extract
zip - package
and compress (archive) files
The zip program
puts one or more compressed files
into a single
zip
archive, along
with information about the files
SYNOPSIS zip options archive inpath inpath
zip accel anaconda-ks.cfg install.log
here a zip file named accel.zip is created from the source file
reboot reboot the system
halt stop the system
poweroff stop the system
shutdown - bring the system down
SYNOPSIS
shutdown [OPTION]... TIME [MESSAGE]
-r
Requests that the system be rebooted after it has been
brought
down.
-c
Cancels a running
shutdown.
-k Only send out the warning messages and
disable logins, do not
actually bring the system down.
lsmod - program to show the
status of modules in the Linux Kernel
uptime - Tell how long the
system has been running.
free - Display amount of free and used memory
in the system
du - estimate file space usage
du [OPTION]... [FILE]...
-h, --human-readable
print sizes in human readable
format (e.g., 1K 234M 2G)
df - report file system disk space
usage
SYNOPSIS
df [OPTION]... [FILE]...
-h, --human-readable
print sizes in human readable
format (e.g., 1K 234M 2G)
uname - print system information
SYNOPSIS
uname [OPTION]..
-a, --all
print all
information, in the following
order, except omit -p
and -i if unknown:
-s, --kernel-name
print the kernel name
-n, --nodename
print the network node hostname
-r, --kernel-release
print the kernel release
# cal
will display the current month of
the current year
# cal 2009
will display the cal of 2009
# cal 10 1987
will display the 10th month of
1987
#history
will display the commands
executed in the particular shell
# history -c
to clear the history
# alias - to assign the shortname
to a command
# alias c=clear
this is only temp
c will perform the function of
clear command
# bc = binary calculator
# bg = to view the process
running at the back ground
# fg n
to bring the process to the fore
ground
where n is the number of the
process that is dispalyed whist executing the command bg.
Links:
1. Links are of two types.
2. a. Hard link
b. Soft link or symbolic link
Hard link:
1. Both the source file and the
destination file will have the same contents.
2. Any number of links can be
created
3. Both the source file and the
destination linked file will have the same inode numbers.
4. If the source file is removed
or deleted unfortunately still the datas can be assessed from the
destination.
5. When hard links are created,
link counts will be increased. And if the hard links are removed
or deleted, link count decreases
automatically.
6. Permissionship on the source
file will have the impact on the destination file permissionship.
7. # ln <source_file>
<destination_file.
Eg: # ln /4students/jai /new
8.
The size of the files (both source and
destination) remains same.
Soft or Symbolic link:
1. Both the source file and the
destination file will have the same contents.
2. But the inode number of the
source file and destination file will be different.
3. The permissionship of the soft
link destination will be differ from the source file.
4. Link count will not be
increased nor decreased.
5. If the source file is deleted,
contents cannot be seen from the destination file.
6. Size of the file will be equal
to the number of the characters of the file name
7. # ln -s <source_file>
<destination_file>
Eg: # ln -s /4students/jai /soft
Editors
vi
vim - vi improved
emac
pico
gedit - graphical editor - works
only with graphics
VI - Editor
# vi - is one of the powerful
editor
used to create a file, edit a
file, view the contents of the file
esc+i - to insert the characters
to the file
esc+A - to bring the cursor to
the end of the line and to add the contents to the line
esc+$ - to bring the cursor to
the end of the line
esc+G - to bring the cursor to
the end of the file
esc+x - to delete a single
character
esc+dw - to delete a single word
esc+dd - to delete a line
esc:n - to move the cursor to the
nth line
esc:10 - to move the cursor to
the 10th line
esc+O - to create a empty line
above the cursor
esc+o - to create a empty line
below the cursor
esc/<keyword> - to search
the keyword
esc:set nu - to set the line
number
esc:set nonu - to remove the line
number
esc+R - to replace the number of
characters
esc+r - to replace a single
character
esc:n,md - to delete number of
lines
where
n = starting line to be deleted
m = end line to be deleted
d = delete the lines
esc:w - to save/write and go back
to the location
esc:q - to quit without saving
the contents to the file
esc:wq - to save and quit from
the file
esc:wq! - to save and quit from
the file forcefully
esc+h - to move the cursor to the
left side
esc+l - to move the cursor to the
right side
esc+k - to move the cursor upward
esc+j - to move the cursor
downward
esc+J - to joinin the line
esc+yy - to copy the line
esc+p - to paste the line
esc+nyy - to copy n number of
lines
esc+5yy - to copy 5 number of
lines from the cursor
esc:nd - to delete the nth line
esc:3d - to delete the 3rd line
esc+I - to bring the cursor to
the beginning of the line
esc+u - undo operation
esc:wq <file-name> - to
save the contents to another file
# vi -R <file-name>
# vi -R new
to open the file as Read Only
# vi -x <file-name>
# vi -x rose
will prompt for the key/password.
the contents of the file will be
encrypted
the contents cannot be seen by
cat or vi editor.
the contents can be seen only by
inserting the option -x with vi editor and by providing the
password.
File Systems
File system refers to the files
and directories stored on a computer. A file system can have different formats
called file system types. These formats determine how the information is stored
as files and directories. Some file system types store redundant copies of the
data, while some file system types make hard drive access faster
Why Share a Common Structure?
The file system structure is the
most basic level of organization in an operating system. Almost all of the ways
an operating system interacts with its users, applications, and security model
are dependent upon the way it organizes files on storage devices. Providing a
common file system structure ensures users and programs are able to access and
write files.
File systems break files down
into two logical categories:
*
Shareable vs. unsharable files
*
Variable vs. static files
Overview of File System Hierarchy
Standard (FHS)
Red Hat Enterprise Linux uses the
Filesystem Hierarchy Standard (FHS) file system structure, which defines the
names, locations, and permissions for many file types and directories.
boot/ Directory
The /boot/ directory contains
static files required to boot the system, such as the Linux kernel. These files
are essential for the system to boot properly.
/dev/ Directory
The /dev/ directory contains
device nodes that either represent devices that are attached to the system or
virtual devices that are provided by the kernel. These device nodes are
essential for the system to function properly. The udev demon takes care of
creating and removing all these device nodes in /dev/.
/etc/ Directory
The /etc/ directory is reserved
for configuration files that are local to the machine. No binaries are to be
placed in /etc/
/lib/ Directory
The /lib/ directory should
contain only those libraries needed to execute the binaries in /bin/ and
/sbin/. These shared library images are particularly important for booting the
system and executing commands within the root file system.
/media/ Directory
The /media/ directory contains
subdirectories used as mount points for removeable media such as usb storage
media, DVDs, CD-ROMs, and Zip disks.
/mnt/ Directory
The /mnt/ directory is reserved
for temporarily mounted file systems, such as NFS file system mounts. For all
removeable media,
opt/ Directory
The /opt/ directory provides
storage for most application software packages
/proc/ Directory
The /proc/ directory contains
special files that either extract information from or send information to the
kernel. Examples include system memory, cpu information, hardware configuration
etc.
/sbin/ Directory
The /sbin/ directory stores
executables used by the root user. The executables in /sbin/ are used at boot
time, for system administration and to perform system recovery operations. Of
this directory
/srv/ Directory
The /srv/ directory contains
site-specific data served by your system running Red Hat Enterprise Linux. This
directory gives users the location of data files for a particular service,
/sys/ Directory
The /sys/ directory utilizes the
new sysfs virtual file system specific to the 2.6 kernel. With the increased
support for hot plug hardware devices in the 2.6 kernel, the /sys/ directory
contains information similarly held in /proc/, but displays a hierarchical view
of specific device information in regards to hot plug devices.
/usr/ Directory
The /usr/ directory is for files
that can be shared across multiple machines. The /usr/ directory is often on
its own partition and is mounted read-only
/usr/local/ Directory
The /usr/local hierarchy is for use by the
system administrator when installing software locally. It needs to be safe from
being overwritten when the system software is updated
/var/ Directory
Since the FHS requires Linux to
mount /usr/ as read-only, any programs that write log files or need spool/ or
lock/ directories should write them to the /var/ directory.
mount - mount a filesystem
All files accessible in a Unix
system are arranged in one big tree, the
file hierarchy, rooted at /. These files can be spread out over
sev-
eral
devices. The mount command serves
to attach the filesystem found
on some device to the big file tree
SYNOPSIS
mount
[-t vfstype] [-o options] device dir
The argument following the -t is used to
indicate the filesystem
type. The
filesystem types which
are currently supported
include: adfs, affs,
autofs, cifs, coda,
coherent, cramfs,
debugfs, devpts, efs, ext, ext2, ext3, ext4,
hfs, hfsplus, hpfs,
iso9660, jfs, minix, msdos,
ncpfs, nfs, nfs4, ntfs, proc, qnx4,
ramfs, reiserfs,
romfs, squashfs, smbfs, sysv, tmpfs, ubifs,
udf, ufs, umsdos, usbfs, vfat,
xenix, xfs, xiafs
The argument following the -o
ro read only
rw read and write
remount to remount the already mounted file system
exec
execute permission
noexec not allowed execution of commands in the
mount file system permission
loop used to mount iso image
mount point it is a directory name that should be created
before mounting of a system
multiple
option separate by comma
mount
flash drive to /media/flash at read &write
mount -t vfat -o rw /dev/sdb1 /media/flash
remount flash drive to /media/flash at read only
mount
-t vfat -o ro,remount /dev/sdb1
/media/flash
mount iso image
using loop command
mount
-o loop /cd1.iso /media
Permanent mounting
To mount a partition
permanently it should be specified in the /etc/fstab file the contents of the
file are in following format
Device file mounting point type (file system) option dump option fsck ption
The first field, (fs_spec),
describes the block
special device or
remote
filesystem to be mounted.The device to be mounted,
like
‘/dev/cdrom’ or
‘/dev/sdb7’. For NFS
mounts one will
have
<host>:<dir>,
Instead of giving the
device explicitly, one may indicate the (ext2
or
xfs) filesystem that is to be mounted by its UUID
or volume label writing LABEL=<label> or
UUID=<uuid>,
e.g., ‘LABEL=Boot’ or
‘UUID=3e6be9de-8139-11d1-9106-a43f08d823a6’.
This will make
the system more robust: adding or removing a
SCSI disk
changes the
disk device name but not the filesystem volume label.
The second field, (fs_file), describes the
mount point for the filesys-
tem.
For swap partitions, this field should be specified as ‘none’.
The third field, (fs_vfstype), describes the
type of
the filesystem.
Linux
supports lots of filesystem types, such as adfs, affs,
autofs,
coda, coherent, cramfs, devpts, efs,
ext2, ext3, hfs, hpfs,
iso9660,
jfs,
minix, msdos, ncpfs,
nfs, ntfs, proc, qnx4, reiserfs, romfs,
smbfs, sysv, tmpfs, udf, ufs, umsdos,
vfat, xenix, xfs,
The fourth field, (fs_mntops), describes the mount
options associated
with the
filesystem.
noauto prevents the indicated file system from
being mounted at a boot time
ro mount the file system read-only ( Commas
must separate options)
rw mount the file system read and write
auto the indicated file system from being
mounted at a boot time
defaults (auto,rw)
The fifth
field, (fs_freq), is
used for these filesystems by the
dump(8) command to determine which
filesystems need to be dumped. If
the
fifth field is not present, a value of zero is returned
and dump
will assume that the filesystem does not
need to be dumped.
The sixth field, (fs_passno), is used by the
fsckprogram to deter-
mine
the order in which filesystem checks are done at reboot time. The
root
filesystem should be specified with a fs_passno of 1,
and other
filesystems should
have a fs_passno of 2.
If the
sixth field is not present or zero, a value
of zero
is returned
and fsck will assume that the filesystem does not need to
be
checked.
mount -a,
--all
Mount
all filesystems (of the given types) mentioned in fstab.
09:08
RDX Master
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