devops-novice

Introduction

We can use commands to interact with the system. These commands can be executed on a terminal to do some task.

---

Getting Started

We will see basic commands which are widely used.

---

pwd - present working directory

pwd

cd - change directory

cd dir - cd to dir

cd / - cd to root

cd ~ - cd to home of current user

cd ../../../ - cd backwards

cd dir1/dir2/dir3 - cd to multiple folders

ls - list contents

ls - list contents of current directory

ls dir1/dir2/dir3 - list contents of dir3

ls *.pdf - list all pdfs

ls *devops* - list all files whose name contains yagna

ls -l - long listing format

ls -t - sort by last modified time

mkdir - create directory

mkdir dir1 - create directory named dir1

mkdir -p dir1/dir2/dir3 - create directory inside directory

rm - remove file

rm filename - remove file with the name filename

rm command will not delete folder, to delete folder use ‘-r’

rm -r dir1 - remove all the contents of dir1, -r will delete all the folders and files inside folders

rm -rf dir1 - remove directory forcefully (-f)

cp - copy file/folder - works like copy-paste - 2 copies will be made

format: cp source destination

cp file1 file2 - create copy of file - change name of file during copy

cp path/of/file1/file1 /path/of/newfile/file1

cp command will not copy folder, to copy folder use ‘-r’

cp -r folder1 folder2 - change name while copy

cp -r folder1 new/path/folder1 - keep same name and copy to different location

ps - report snapshot of current processes

ps -ef - get all the processes

Output of ps -ef will be as follows

PID TTY TIME CMD

• PID - Process ID of the process - you can use this ID to kill/stop the process

• TTY - The terminal from which the process (or its parent) was started. A question mark indicates there is no controlling terminal.

• TIME - The total amount of CPU time used by the process since it began.

• CMD - Command that generates the process

grep - searches for pattern

grep "SEARCH STRING" filename

grep -r "SEARCH STRING" . - search string in all files and folders in current folder

grep -r "SEARCH STRING" path/of/the/folder - search string in all the files in given path

grep -e "SEARCH PATTERN" filename or folder - example grep -e "*g" filename - search anything ending with g

grep -v "SKIP PATTERN" filename or folder - skip the pattern and show remaining result

cat - see contents of file

cat filename

cat path/to/some/folder/filename

cat and grep

cat and grep can be used together to search a string

cat filename | grep "SEARCH STRING" - all above grep commands can be used after the pipe ‘

’

File permissions

Every file/folder in Linux have specific permission which describe security for the file.

For example ‘drwxr-xr-x’ is the file permission.

• First character states the file type

Next 9 characters are for file permissions which can be divided into 3 parts.

• First 3 - read, write, execute for user

• Next 3 - read, write, execute for group

• Last 3 - read, write, execute for others

For example the permission ‘drwxr-xrw-‘ means that

1. given type is directory (d)
2. user has read, write, execute permissions (rwx)
3. group has read, execute permissions (r-x)
4. others have read, write permissions (rw-)

Change file permissions

chmod is used to change file permissions

To change directory permissions in Linux, use the following:

• chmod +rwx filename to add permissions

• chmod -rwx directoryname to remove permissions.

• chmod +x filename to allow executable permissions.

• chmod -wx filename to take out write and executable permissions.

Note that “r” is for read, “w” is for write, and “x” is for execute.