Sunday, November 22, 2015

Linux Essentails

Linux directory structure

 /                          "Root" "Slash"
/bin                      Binaries files or executable files
/etc                      Configuration files
/home                  User home directory, separate user data (pics etc)
/home/shannan   User Shannan home directory
/root                    Home directory for root account.
/opt                     Third-party software (google earth gets installed)
/tmp                    Temporary space (OS cleans these directory at boot time)
/usr                      User related programs lives
/var                     Variable data (logs files). Things that change often
/cdrom                Mount point for CD-ROM
/boot                   Files needed to boot OS
/lib                      System libraries
/lost+found        Used by the filesystem keep recovered files after check has been performed
/mnt                   Used for mounting external file systems
/proc                  Info about running processes
/sbin                  System Administration binaries
/selinux             Display info about SELINUX
/srv                    Contains data which is served by the systems
/srv/www          Webserver files
/srv/ftp              FTP files

$   typical user prompt
#   root user prompt

Root user can do all things
Normal user account can do subset of things

Basic Linux Commands
  commands are case sensitive
  ls, cd, pwd, cat, echo, man, exit, clear

man ls --> space, enter, g, G

Environmental Variables
  Storage location with name/value
  Name typically uppercase
  Print value $VAR_NAME
  Locate command "which ls"

.     current dir
..     parent dir
cd - previous dir
./     execute command in the current dir
/opt/command/cat    executes cat file in the dir

Creating/Removing directories
mkdir [-p]  directory - Create dir
rmdir [-p]  directory  - Remove dir
rm -rf        directory  - Recursively remove all

ls -l
 permissions links user groups size modified-date name
 -  file
 d dir
 l  symbolic link
 r  read
 w write
 x  execute
 three sets of permissions user, group, other

  chmod ugao (user group all other) +(add) -(remove) =(set) x(execute) file

find command
 find path expression

find / -iname  dchq  (ignore case)
find / -iname  *dchq  (ignore case)

tail -50 filename (print last 50 lines)
tail -50f filename (print last 50 lines and follows the file)

vi has modes (command, insert, line)
command (h j k l)
insert (i)
line (:no) :$ last line
shift + 6 is beginning of line
shift + $ is end of line

c create
x extract
z compression
f file
t list
v verbose

tar cf bkp.tar abc
tar tf bkp.tar (prints files)
tar xf bkp.tar (extracts file)
tar zcf bkp.tar.gz or bkp.tgz


du -h

IO Redirection
Output redirection
ls -lrt > files.txt
ls -lrt >> files.txt (appends)
ls -lrt 1> files.txt  (0 is standard input, 1 output, 2 error)
lss -lrt 2> files.txt (standard error)
lss -lrt 2> /dev/null (standard error)
ls -lrt 1> files.txt 2>&1 (standard error is also going to files.txt)

input redirection
sort < files.txt

grep (search file contents)
grep abc file.txt
grep -i abc file.txt (ignore case)

crontab -l
crontab file

su (switch user)
sudo (super user do) execute command as other user

Packages & Package Managers

package is collection of files for an application
Package Managers - installs, updates, remove packages
RPM (RHEL, CentOS, Oracle Linux, Fedora, Scientific Linux) Redhat Package Manager
yum search
yum install yum install -y
yum info
yum remove

rpm -ql (list)
rpm -ivh (install)
rpm -e (remove)

DEB Distro
apt (Advance packaging tool)

apt-get install -y
apt-get remove -y