Cloud DevOps Admin Guide

when we run a command with a typo, we can correct the typo and re-run the command by the following command.

^wrong^right

Here are the examples:

The man command is wrongly typed as many
[root@test /]# many head
-bash: many: command not found


The y is replaced with empty character.
[root@test /]# ^y
man head

--------------------------------------------------------------
Here man is typed as men

[root@test /]# men head
-bash: men: command not found
the letter e is replaced with a and then the command executes.
[root@test /]# ^e^a
man head

Push your present working directory to a stack that you can pop later

If are a Bash user and you are in a directory and need to go else where for a while but don't want to lose where you were, use pushd instead of cd.

cd /home/complicated/path/.I/dont/want/to/forget

pushd /tmp

cd thing/in/tmp

popd (returns you to /home/complicated/path/.I/dont/want/to/forget)

Print column1, column5 and column7 of a data file or output of any columns list

$awk ‘{print $1, $5, $7}’ data_file

$cat file_name |awk ‘{print $1 $5 $7}’

$ls –al |awk ‘{print $1, $5, $7}’ -- Prints file_permissions,size and date

Syntax of running an awk program

Awk ‘program’ input file(s)

List all files names whose file size greater than zero.

$ls –al |awk ‘$5 > 0 {print $9}’

List all files whose file size equal to 512bytes.

$ls –al |awk ‘$5 == 512 {print $9}’

print all lines

$awk ‘{print }’ file_name

$awk ‘{print 0}’ file_name

Number of lines in a file

$awk ‘ END {print NR}’ file_name

Number of columns in each row of a file

$awk ‘ {print NF’} file_name

Sort the output of file and eliminate duplicate rows

$awk ‘{print $1, $5, $7}’ |sort –u

List all file names whose file size is greater than 512bytes and owner is "oracle"

$ls –al |awk ‘$3 == "oracle" && $5 > 512 {print $9}’

List all file names whose owner could be either "oracle" or "root"

$ls –al |awk ‘$3 == "oracle" || $3 == "root" {print $9}’

list all the files whose owner is not "oracle

$ls –al |awk ‘$3 != "oracle" {print $9}’

List all lines which has atlease one or more characters

$awk ‘NF > 0 {print }’ file_name

List all lines longer that 50 characters

$awk ‘length($0) > 50 ‘{print }’ file_name

List first two columns

$awk ‘{print $1, $2}’ file_name
Swap first two columns of a file and print

$awk ‘{temp = $1; $1 = $2; $2 = temp; print }’ file_name

Replace first column as "ORACLE" in a data file

$awk ‘{$1 = "ORACLE"; print }’ data_file
Remove first column values in a data file

$awk ‘{$1 =""; print }’ data_file

Calculate total size of a directory in Mb

$ls –al |awk ‘{total +=$5};END {print "Total size: " total/1024/1024 " Mb"}’

Calculate total size of a directory including sub directories in Mb

$ls –lR |awk ‘{total +=$5};END {print "Total size: " total/1024/1024 " Mb"}’

Find largest file in a directory including sub directories

$ls –lR |awk ‘{print $5 "\t" $9}’ |sort –n |tail -1

/unix is a symbolic link to the booted kernel. To find out what kernel mode is running, enter ls -l /unix and see what file /unix it links to.
The following are the three possible outputs from the ls -l /unix command and their  corresponding kernels:

/unix -> /usr/lib/boot/unix_up                                                            # 32 bit uniprocessor kernel
/unix -> /usr/lib/boot/unix_mp                                                           # 32 bit multiprocessor kernel
/unix -> /usr/lib/boot/unix_64                                                            # 64 bit multiprocessor kernel

For memory information, we use the command svmon.
svmon shows the total usage of physical and paging memory.

Command to display top ten processes and users
svmon -P -v -t 10 | more

Displaying top CPU_consuming processes:
ps aux | head -1; ps aux | sort -rn +2
Displaying top memory-consuming processes:
ps aux | head -1; ps aux | sort -rn +3 | head

Displaying process in order of priority:
ps -eakl | sort -n +6 | head

Displaying the process in order of time
ps vx | head -1;ps vx | grep -v PID | sort -rn +3

Displaying the process in order of real memory use
ps vx | head -1; ps vx | grep -v PID | sort -rn +6

Displaying the process in order of I/O
ps vx | head -1; ps vx | grep -v PID | sort -rn +4

Prepending one or more spaces to your command won't be saved in history.
It i very useful for hiding your commands which consists of passwords on the commandline.
This is tested in bash shell and works successfully.

Example :
$ echo this goes to history
this goes to history

$ echo this wont go to history
this wont go to history

$ history
1 echo this goes to history
2 history

The manual page of "bash" shows as follows:

 HISTCONTROL
         A  colon-separated  list of values controlling how commands are
         saved on the history list.  If  the  list  of  values  includes
         ignorespace,  lines  which begin with a space character are not
         saved in the history list.  A value of ignoredups causes  lines
         matching  the  previous history entry to not be saved.  A value
         of ignoreboth is shorthand for ignorespace and  ignoredups.   A
         value  of erasedups causes all previous lines matching the cur‐
         rent line to be removed from the history list before that  line
         is  saved.   Any  value  not  in the above list is ignored.  If
         HISTCONTROL is unset, or does not include a  valid  value,  all
         lines  read  by the shell parser are saved on the history list,
         subject to the value of HISTIGNORE.  The second and  subsequent
         lines  of a multi-line compound command are not tested, and are
         added to the history regardless of the value of HISTCONTROL. 

Exit without saving history

kill -9 $$

this exits bash without saving the history. unlike explicitly disabling the history in some way, this works anywhere, and it works if you decide *after* issuing the command you don't want logged, that you don't want it logged

... $ ( or ${$} ) is the pid of the current bash instance

this also works perfectly in shells that don't have $ if you do something like

kill -9 `readlink /proc/self`