By

Contents
  1. 1. CentOS quck start guide
  • Analyzing syslog entries
    1. 1. 1. Stop and Start RHEL7 firewall
    2. 2. 2. Disable and Enable RHEL7 firewall
    3. 3. 3. Set hostname
  • Signals
    1. SIGKILL signal
    2. SIGHUP signal
    3. Bash Shell Variables
    4. Bash Shell Scripting
      1. 1. Functions
      2. 2. if
      3. 3. file or diri tests
      4. 4. else statement
      5. 5. if elif statement
      6. 6. Loops statement
      7. 7. Automate script execution
    5. Working in the shell efficiently
      1. 1. Command Editing Shortcuts
      2. 2. Command Recall Shortcuts
      3. 3. Command Control Shortcuts
      4. 4. for debuging purpose
      5. 5. Bash Bang (!) Commands

    • CentOS quck start guide

    Analyzing syslog entries

    log file standard format

    1. Stop and Start RHEL7 firewall

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    [root@rhel7 ~]# service firewalld stop
    Redirecting to /bin/systemctl stop  firewalld.service

    [root@rhel7 ~]# service firewalld start
    Redirecting to /bin/systemctl start  firewalld.service

    2. Disable and Enable RHEL7 firewall

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    [root@rhel7 ~]# systemctl disable firewalld
    rm '/etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service'
    rm '/etc/systemd/system/basic.target.wants/firewalld.service'


    [root@rhel7 ~]# systemctl enable firewalld
    ln -s '/usr/lib/systemd/system/firewalld.service' '/etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service'
    ln -s '/usr/lib/systemd/system/firewalld.service' '/etc/systemd/system/basic.target.wants/firewalld.service'

    3. Set hostname

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    [root@rhel7 ~]# hostnamectl

    [root@rhel7 ~]# hostnamectl set-hostname nameyoulike

    Signals

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    [root@ip-172-31-5-191 ~]# kill -l
     1) SIGHUP	 2) SIGINT	 3) SIGQUIT	 4) SIGILL	 5) SIGTRAP
     6) SIGABRT	 7) SIGBUS	 8) SIGFPE	 9) SIGKILL	10) SIGUSR1
    11) SIGSEGV	12) SIGUSR2	13) SIGPIPE	14) SIGALRM	15) SIGTERM
    16) SIGSTKFLT	17) SIGCHLD	18) SIGCONT	19) SIGSTOP	20) SIGTSTP
    21) SIGTTIN	22) SIGTTOU	23) SIGURG	24) SIGXCPU	25) SIGXFSZ
    26) SIGVTALRM	27) SIGPROF	28) SIGWINCH	29) SIGIO	30) SIGPWR
    31) SIGSYS	34) SIGRTMIN	35) SIGRTMIN+1	36) SIGRTMIN+2	37) SIGRTMIN+3
    38) SIGRTMIN+4	39) SIGRTMIN+5	40) SIGRTMIN+6	41) SIGRTMIN+7	42) SIGRTMIN+8
    43) SIGRTMIN+9	44) SIGRTMIN+10	45) SIGRTMIN+11	46) SIGRTMIN+12	47) SIGRTMIN+13
    48) SIGRTMIN+14	49) SIGRTMIN+15	50) SIGRTMAX-14	51) SIGRTMAX-13	52) SIGRTMAX-12
    53) SIGRTMAX-11	54) SIGRTMAX-10	55) SIGRTMAX-9	56) SIGRTMAX-8	57) SIGRTMAX-7
    58) SIGRTMAX-6	59) SIGRTMAX-5	60) SIGRTMAX-4	61) SIGRTMAX-3	62) SIGRTMAX-2
    63) SIGRTMAX-1	64) SIGRTMAX

    SIGKILL signal

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    [root@ip-172-31-5-191 ~]# sleep 10000 &
    [1] 19559
    [root@ip-172-31-5-191 ~]# ps aux|grep sleep
    root     19559  0.0  0.0 107952   356 pts/0    S    07:48   0:00 sleep 10000
    root     19564  0.0  0.0 112708   976 pts/0    S+   07:48   0:00 grep --color=auto sleep
    [root@ip-172-31-5-191 ~]# kill -9 19559
    [1]+  Killed                  sleep 10000
    [root@ip-172-31-5-191 ~]# ps aux|grep sleep
    root     19596  0.0  0.0 112708   980 pts/0    S+   07:49   0:00 grep --color=auto sleep

    SIGHUP signal

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    [root@ip-172-31-5-191 ~]# nohup sleep 1000 &
    [1] 19786
    [root@ip-172-31-5-191 ~]# nohup: ignoring input and appending output to ‘nohup.out’

    Bash Shell Variables

    Put variable into the file /etc/environment

    Another very important rule is that a child process will never be able to change the parent’s environment variables, because the child and parent are independent from each other and the child only has a local copy of the parent’s environment:

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    [root@ip-172-31-5-191 ~]# mkdir ~/scripts
    [root@ip-172-31-5-191 ~]# printf '#!/bin/bash\nexport CHILDVAR=Hello_from_child\n' > ~/scripts/child.sh
    [root@ip-172-31-5-191 ~]# cat ~/scripts/child.sh
    #!/bin/bash
    export CHILDVAR=Hello_from_child
    [root@ip-172-31-5-191 ~]# chmod +x ~/scripts/child.sh
    [root@ip-172-31-5-191 ~]# ~/scripts/child.sh
    [root@ip-172-31-5-191 ~]# echo $CHILDVAR

    Bash Shell Scripting

    Functions

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    [root@ip-172-31-5-191 ~]# say_hello() {
    > echo "My name is $1";
    > }

    [root@ip-172-31-5-191 ~]# say_hello Stan
    My name is Stan
    [root@ip-172-31-5-191 ~]# say_another_thing() {
    > say_hello Stan
    > echo "I like CentOS 7";
    > }

    [root@ip-172-31-5-191 ~]# say_another_thing
    My name is Stan
    I like CentOS 7
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    [root@ip-172-31-5-191 ~]# cat run.sh
    #!/bin/bash
    echo "Hello world"
    echo "-----------"
    if [[ $# -lt 2 ]]
    then
      echo "Usage $0 param1 param2"
      exit 1
    fi
    echo $1
    echo $2
    echo $0
    echo $#
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    [root@ip-172-31-5-191 ~]# PASSWORD="tt4321"
    [root@ip-172-31-5-191 ~]# if [[ $PASSWORD -eq "hello_world" || $PASSWORD -eq "tt4321" ]]; then echo "password correct"; fi
    password correct

    if

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    if [[ $EXIT -eq 0 ]]
    if ! [[ $EXIT -eq 0 ]]
    if [[ $PASSWORD == "Hello_world" ]]
    if [[ $PASSWORD -eq "hello_world" || $PASSWORD -eq "tt4321" ]]

    STRING="Lorem ipsum dolor sit"
    if [[ $STRING =~ ^..rem ]]
    if [[ $NUMBER -lt 10 ]]  ##-lt less than
    if [[ $NUMBER -gt 10 ]]  ##-gt greater than

    file or diri tests

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    if [[ -a $FILE ]]
    if [[ -d $DIR ]]

    for read the bash manual
    man bash /CONDITIONAL EXPRESSIONS

    else statement

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    if [[ $EXIT -eq 0 ]]
    then
      echo "whatever"
    else
      echo "cannot access the files"
    fi

    if elif statement

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    if [[ $VALUE -gt 5 ]]
    then
      echo "value is bigger than 5"
    elif [[ $VALUE -eq 5 ]]
    then 
      echo "value is equal to 5"
    elif [[ $VALUE -lt 5 ]]
    then
      echo "value is less than 5"
    fi

    Loops statement

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    for count in 1 2 3 4
    do
      echo $count
    done

    for number in $(seq 1 20)
    do
     echo "This is $number"
    done

    for number in {1..20}
    do
     echo "This is $number"
    done

    change multi file names

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    mkdir ~/stuff
    touch ~/stuff/1.txt ~/stuff/2.txt ~/stuff/3.txt ~/stuff/4.txt ~/stuff/5.txt
    for file in ~/stuff/*.txt
    do
      mv $file ~/stuff/$(basename $file .txt).doc
    done

    Automate script execution

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    cat scripts/motd-commandlinefu-update.sh
    #!/bin/bash
    wget -O /etc/motd http://www.commandlinefu.com/commands/random/plaintext
    ls /etc/cron* -d
    /etc/cron.d  /etc/cron.daily  /etc/cron.hourly  /etc/cron.monthly  /etc/crontab  /etc/cron.weekly
    root@stan-OptiPlex-380:~|⇒  cd /etc/cron.daily
    root@stan-OptiPlex-380:/etc/cron.daily|
    ⇒  ln -s /root/scripts/motd-commandlinefu-update.sh
    root@stan-OptiPlex-380:/etc/cron.daily|
    ⇒  ll
    total 72
    drwxr-xr-x   2 root root  4096 Jun 20 10:47 ./
    drwxr-xr-x 150 root root 12288 Jun 20 10:44 ../
    -rwxr-xr-x   1 root root   311 May 30  2017 0anacron*
    -rwxr-xr-x   1 root root   539 Oct 11  2018 apache2*
    -rwxr-xr-x   1 root root   376 Nov 21  2017 apport*
    -rwxr-xr-x   1 root root  1478 Apr 20  2018 apt-compat*
    -rwxr-xr-x   1 root root   314 Jan 17  2018 aptitude*
    -rwxr-xr-x   1 root root   355 Dec 29  2017 bsdmainutils*
    -rwxr-xr-x   1 root root   384 Dec 13  2012 cracklib-runtime*
    -rwxr-xr-x   1 root root  1176 Nov  3  2017 dpkg*
    -rwxr-xr-x   1 root root   372 Aug 22  2017 logrotate*
    -rwxr-xr-x   1 root root  1065 Apr  7  2018 man-db*
    -rwxr-xr-x   1 root root   538 Mar  2  2018 mlocate*
    lrwxrwxrwx   1 root root    42 Jun 20 10:47 motd-commandlinefu-update.sh -> /root/scripts/motd-commandlinefu-update.sh*
    -rwxr-xr-x   1 root root   249 Jan 26  2018 passwd*
    -rw-r--r--   1 root root   102 Nov 16  2017 .placeholder
    -rwxr-xr-x   1 root root   246 Mar 22  2018 ubuntu-advantage-tools*

    Working in the shell efficiently

    man bash /Commands for Moving

    Command Editing Shortcuts

    • Ctrl + a – go to the start of the command line

    • Ctrl + e – go to the end of the command line

    • Ctrl + k – delete from cursor to the end of the command line

    • Ctrl + u – delete from cursor to the start of the command line

    • Ctrl + w – delete from cursor to start of word (i.e. delete backwards one word)

    • Ctrl + y – paste word or text that was cut using one of the deletion shortcuts (such as the one above) after the cursor

    • Ctrl + xx – move between start of command line and current cursor position (and back again)

    • Alt + b – move backward one word (or go to start of word the cursor is currently on)

    • Alt + f – move forward one word (or go to end of word the cursor is currently on)

    • Alt + d – delete to end of word starting at cursor (whole word if cursor is at the beginning of word)

    • Alt + c – capitalize to end of word starting at cursor (whole word if cursor is at the beginning of word)

    • Alt + u – make uppercase from cursor to end of word

    • Alt + l – make lowercase from cursor to end of word

    • Alt + t – swap current word with previous

    • Alt + . – print previous command’s argument

    • Ctrl + f – move forward one character

    • Ctrl + b – move backward one character

    • Ctrl + d – delete character under the cursor

    • Ctrl + h – delete character before the cursor

    • Ctrl + t – swap character under cursor with the previous one

      Command Recall Shortcuts

    • Ctrl + r – search the history backwards

    • Ctrl + g – escape from history searching mode

    • Ctrl + p – previous command in history (i.e. walk back through the command history)

    • Ctrl + n – next command in history (i.e. walk forward through the command history)

    • Alt + . – use the last word of the previous command

      Command Control Shortcuts

    • Ctrl + l – clear the screen

    • Ctrl + s – stops the output to the screen (for long running verbose command)

    • Ctrl + q – allow output to the screen (if previously stopped using command above)

    • Ctrl + c – terminate the command

    • Ctrl + z – suspend/stop the command

      for debuging purpose

    • Ctrl + Alt + e - $SHELL /bin/bash

      Bash Bang (!) Commands

      Bash also has some handy features that use the ! (bang) to allow you to do some funky stuff with bash commands.

    • !! – run last command

    • !blah – run the most recent command that starts with ‘blah’ (e.g. !ls)

    • !blah:p – print out the command that !blah would run (also adds it as the latest command in the command history)

    • !$ – the last word of the previous command (same as Alt + .)

    • !$:p – print out the word that !$ would substitute

    • !* – the previous command except for the last word (e.g. if you type ‘_find somefile.txt /’, then !* would give you ‘_find somefile.txt’)

    • !*:p – print out what !* would substitute

    • tail -f log_file | egrep -v 'ELB|Pingdom|Health' – filter out stuff has certain keywords

    Contents
    1. 1. CentOS quck start guide
  • Analyzing syslog entries
    1. 1. 1. Stop and Start RHEL7 firewall
    2. 2. 2. Disable and Enable RHEL7 firewall
    3. 3. 3. Set hostname
  • Signals
    1. SIGKILL signal
    2. SIGHUP signal
    3. Bash Shell Variables
    4. Bash Shell Scripting
      1. 1. Functions
      2. 2. if
      3. 3. file or diri tests
      4. 4. else statement
      5. 5. if elif statement
      6. 6. Loops statement
      7. 7. Automate script execution
    5. Working in the shell efficiently
      1. 1. Command Editing Shortcuts
      2. 2. Command Recall Shortcuts
      3. 3. Command Control Shortcuts
      4. 4. for debuging purpose
      5. 5. Bash Bang (!) Commands