4/15/2018 - 1:49 PM

Linux Commands

ls * list file and directory
ls  -l *long list file and directory , ll
ls -R *listing the file and directory with recurrsive.
ls -laR
pwd  *present working direcory
cd dirname  *enter a directory
cd.. back one directory cd - * to enter
cd ../.. *two level dir back
cd/ *root partition
cd and enter * to enter users home directory , "cd~"
rm filename *Remove file
rmdir directory_name * Remove directory (If empty)
rm -r dirname *Remove directory (If not empty) (r -> recurrsive).
rm -rf dirname *Remove directory and file forcefully.
cp filename destination_address  *to copy file.
cp -a dirname destination_address *to copy directory.
mv - filename/dirname newname *to rename
mv - filename/dirname  destination_address *to move file or directory. 

Command /syntax
 command option argument
[root@localhost Desktop]#
 user  machine  using dir root user
 $ Local user

useradd username or  adduser username (with root permissions only)
to chg password -> passwd username
#newpassword ******

File System Hierarchy
/ is root directory
/bin user essential commands
/sbin Superuser essential commands
/dev to store device files
/boot Its a bootloader (to store required booting file) Grub2 (Grand unified Bootloader)
/etc to store configuration file.
/root root user data.
/tmp temporary directory (after 10 days file will be deleted automatically)
/usr to install programs.
/var Its a variable data (different types of files available ) 
/var/log for logs  /var/tmp after 30 days /var/spool/mail mail
/run/media removable drives (For rhel 6 and old in /media directly)

vim - Text Editor.
1.) Command Mode  vim filename.
2.)Insert Mode - Edit or Modify file . press 'i' or Insert key.
3.)Ex Mode close a file with saving or not saving. ESC key
    to save file :wq (close file with save)
    :wq! (save forcefully)
    :q (without saving)
    ESC o open a new line below from cursor
    ESC u undo
    ctrl + r redo
    ESC n yy
             no of lines yy(yanked)
    ESC p paste copied data 
    ESC :7,12 copy between lines
    Search and replace ->  :%s/oldwordname/newname/g
                                                   search                                      global
    ESC /word_name to search a word      n-> next find match word shift+n -> previous
    ESC :nohl No Highlighted
    ESC :set nu to set line numbers
    ESC :set nonu remove or unset line numbers
    ESC gg  First line
    ESC shift+g last line
    ESC :line_number

    View content of a file
    cat filename
    less filename view content page wise
    more filename view content page wise show % studied
    head filename    (first 10 lines)
    head -n3 filename    (first n lines)
    tail filename    (last 10 lines)
    head -n3 filename    (last n lines)
    wc filename (show line,word,size)

    whatis cmd_name
    man cmd_Name
    info cmd_Name more details then man
    which cmd_Name from where cmmd is running
    rpm -q -f /usr/bin/mv  to know the package

    Users and Groups : 
    3 types of users
    1.) SuperUser - rootuser user Id '0'
    2.)System user -to manage and create system services.
    3.)Regular user/local start from 1000(RHEL7) 500(Rhel 6)
    1-201 (Static-Id) 201-999(dynamic Id)

    id - current user id
    id username - user id

    userdel  -r username  delete user
    usermod -L username 
    usermod -U username
    usermod -l newname oldname
    chfn username - change info about user
    chage -l username to check age on an user
    chage -E "days/weeks/year" username expire
    chage -E -1 username unexpire

    chage -m 5 -M 45 -I 3 -W 2 mustfzz           *min max inactive warning
    chage -m 0 -M 99999 -I -1 -W 7 mustfzz   *bring back to original

Group Users
groupAdd group_name
groupmod -n newname oldname
usermod -G groupname username
usermod -G groupname,group2,group3 username
gpasswd -M user1,user2,user3 groupname

groupmems -g groupname -l *list of user in a group
groupmems -d username -g groupname  *delete user from group
groups mustfzz display group info


userfields in passwd file 7

password stored in /etc/shadow stores username/password/age information
shadow has 9 fields.

Linux File System Permissions

File has three categories
1.) User
2.) Group
3.) Others

UMASK controls the permission automatically

permissions r-w-x
file     dir
rwx   rwx
---     rx

      -                        ---                              ---                                      ---                      .              +
file_type : User_permission : Group_premission :  Other_permission                   ACL

_ file
d dir
l Link File
b block file          |
c character file  |    =>h/w device (in /dev)
p pipe file            |
s socket file        |

Switch User (from one to another from terminal) 
su - username

who - u,g,o,a
what - +,-,=
which - r,w,x

cmmd/syntax -  chmod whoWhatWhich file/dir_name
                               chmod g+w file/dir_name
                               chmod -R whoWhatWhich file/dir_name
                               chmod -R g+w file/dir_name
                               chmod go+wx file/dir
                               chmod a+rwx file/dir
                               chmod  g+wx,o-rx file/dir       


stat file/dir show the permissions of file/dir in symbolic  and  numeric method

Changing User and Group Ownership

chown user/owner_name file/directory_name      * change ownership
chown -R user/owner_name file/directory_name   * Reccurrsive

chgrp group_name file/dir
chown username:groupname file/dir_name * to change user and group ownership (-R for reccurrsive)

Special Permissions

1.) Suid  (Set user id) - when only particular user can execute. this time permission apply on user execution position. (i.e. in place of --x). 
   Symbol - 's' and no. 4 .  It can only be applied to file.
   ex:  _rwsr_xr_x
         chmod 4755 
                       here  4 is for special permissions.

2.) Sgid 
sgid assign on group execute position that mean place of x
when sgid is set on a directory then files new created in the directory have there group owner set to match the group owner of the directory.

symbol - 's' and no. 2 
Ex  chmod 2775 directory

3.) Sticky 
      It assings on a directory
      It assign on other execute postion.
      When sticky is set on a directory then file/dir created under this directory , then
      only file/dir deleted by only owner.
     Symbol 't' and no. '1'
     EX:  chmod 1757 litc/a

Break Root Password
Rhel 6
Enter in kernel mode by s
passwt root
and then  Enter the new password
Rhel 7
ctrl+alt+del then e
take to linux16 then to end and rd.break

Archiving files creating and Compressing
Tar (tape archive)
The archive file creates from Tar command.

tar -cvf filename.tar files/dirname
        create verbose file
tar -tvf filename.tar
        to list file/dir from 
 tar -rvf filename.tar       
        to add files and directory if already archive file existing
 tar -xvf filename.tar
        to  restore  particular file and directory from archive file
After Tar
1.)  gzip   | gzip filename.tar
                  gunzip filename.tar.gz
2.) bzip2 | bzip2 filename.tar
                  bunzip filename.tar.bz2
3.) xz |      xz filename.tar
                  unxz filename.tar.xz

tar -czvf filename.tar.gz  file/dirname -> gzip
tar -cjvf filename.tar.bz2  file/dirname -> bzip2
tar -cJvf filename.tar.xz  file/dirname -> xz

It is a value that controls file/dir permission.
without umask file permission  666  | directory permission 777
localuser mask 002 and root user mask 022

to calculate umask  Default Mask - Required Mask
 [u1@localhost ~]$ vim ~/.bash
[u1@localhost ~]$ vim ~/.bashrc
add umask 007 at the end

Permanent for all user 
root user 
vim /etc/bashrc
change 002 to 007
Repeat the same for /etc/profile

ACL (Access Contol List)

when we want to multiple permission assing one a single target file/dir and access by user and group then we can implement  ACL.

getfacl file/dir * to get acl info
setfacl  -m u:username:permission file/dirname * set acl
setfacl  -m g:groupname:permission file/dirname * set acl
 on group

EX: setfacl  -m u:mustfzz:rw file/dirname

setfacl  -x u:username file/dirname * remove permissions

setfacl -b file/dirname * remove all acl

Link - Hard Link and  Soft Link
1.) can create only within a partition      1.) can create accross the partition
2.) Inode number will be the same         2.) Inode number are different
3.) original and link file are in  same size. 3.) size is less than original file.
4.) If original file is removed then we can access the link file  4.) Link file can not be accessed
5.) Only for file             5.) for file and directory.

Link is an another name of our original file.
df -TH * show partitions
ls -il file/dirname * show inode number

ln file/dirname link-file/dirname
unlick file/dirname * unlink and file will be deleted

Find Files and Directory
by name  * -name
by size     * -size 10m | +5m | -5m
by permission * -perm 755
by ownername and ownership * -user username
by groupname * -group groupname 
by uid and gid
by File-Type * -type f(file) d(directory) l(linked) b(block) c() p(pipeline) s(socket)
                          particular extention *.txt
by  no of days access time * atime 5days | +5days | - days
by no of minutes  * amin | mmin (m for modification time).
by links * find / -type f -links 2 | +2 | -2 

Search and save file
find / - user mustfzz -exec cp -av {} /destination_address \;
find path file/dirname    * whole system
find /etc file/dirname    * particular directory
find -name file/dirname * working directory

Using Grep
to find particular string

grep stringname filename
grep --color stringname filename 8 with color for rhel 6
grep ^stringname filename | start
grep stringname$ filename | end

grep -e stringname -e stringname filename
grep --color stringname filename >> path/filename 

Sudo gives root priveledges to the local user.
If any is a member of wheel group It can execute root commands.
vim /etc/sudoers

Lan Cable
1) Cross-over cale
2) Straight cable
3) Roll-over cable /console cable


class - A 1-127
class - B 128-191
class - C 192-223
class - D 224-239
class - E 240-255

Private Ip Range

class - A
 class - B
class - C

Subnet Mask

Its a property of IP address.
class - A                    /8
class - B                /16
class - C           /24

CIDR (Class-Less Inter Domain Routing)

Total Host and Total N/W in each classes

class A 1     00000001
              127 0111111111

2^7 = 127 N/W
2^24 = 16777216-2 = 16777214

Class B
            128 10000000
            191  10111111 
 2^14  = 16384 N\W
 2^16  = 65534 Total host
              65532 Valid host

Class C
            192  11000000
            223  10111111 
 2^21  = 16384 N\W
 2^8  = 256 Total host
            254 Valid host
CIDR (/8-/32 {/9-/30}) and Subnet Mask calculation.
/14             255..252.0.0

Subnetting :
To breakup large network into small using subnetting.
1.) Class IP-Address
2.)Subnet MAsk
3.)Blocksize (256-Mask)
4.)Subnetwork id -(First valued Host | Last Valued Host | Broadcast Address )
5.)Total Host on each subnetwork id -  2^x-2 x= off bit of host part.
6.)Total Subnetwork id 2^y where y = on bit of host part.

class c
1.)  /26
2.)subnet mask
3.)block size 256-192 = 64
4.)subnet id 
                                                                    FVH           LVH           B/C
                                     10.1             10.62         10.63
                                   10.65          10.126        10.127
                                  10.129       10.190        10.191
                                  10.193        10.254       10.255
5.)Total Host on each subnetwork id  = 2^6-2=62                            
6.) TOTAL SUBNET ID 2^2 =4      

N/W address
IP address
Subnet Mask

Rhel 6

service network restart
cat e