/bash-scripts

This repository contains various scripts utilizing Linux commands and techniques, such as awk, grep, egrep, ping, usermod, sed, ps, kill, and useradd. The scripts serve various purposes, including logging messages related to defined keywords, checking directories and files, copying files to remote hosts, disabling inactive user accounts, managing

Primary LanguageShell

Description

This repository contains various scripts comprising of various techniques and linux commands (awk, grep,egrep, ping, usermod, sed, ps, kill, useradd):

  • central-logger.bash >>>>>> This script will log messages related to only defined keywords like: "refused|invalid|error|fail|lost|shut|down|offline"
  • check-dir.bash >>>>>> This script will find directories without users or unknown user
  • check-file-system.bash >>>>>> This script will check for disk space
  • check-files.bash >>>>>> This script will check whether given files are present in the system
  • copy-files-to-remote.bash >>>>>> This script will copy files to remote hosts
  • disable-users-for.bash >>>>>> This script will disable inactive user accounts using for loop
  • disable-users-xargs.bash >>>>>> This script will disable inactive user accounts with xargs
  • inventory-add-record.bash >>>>>> This system will add a system inventory to the database file
  • inventory-delete-record.bash >>>>>> This script will delete system from inventory database file
  • kill-process.bash >>>>>> This script will find dead or zombie process and kill them
  • list-users-by-input.bash >>>>>> This script will list users logged in by user input of date
  • list-users.bash >>>>>> This script will list users logged in today
  • log-alert.bash >>>>>> This script will send an email to administrator
  • rename-file.bash >>>>>> Rename files ending with .txt
  • total-num-files.bash >>>>>> This script will verify total no. of files
  • user-add-automation.bash >>>>>> This script will check if the user already exists, if not will create along with description specified by -c, and userid is specified by -u

Notes

Cron Job

  • Description: A cron job is a automated servvice in linux that you can use to run a script in schedule, Moreover you can notiy someone using email/sendmail
  • Usage: crontab -e [to edit user's crontab]
  • Values provided for [m h dom mon dow command] (minute (m), hour (h), day of month (dom), month (mon), and day of week (dow))
  • You might need to add yourself to the crontab user group using: usermod -a -G crontab (username)

Extra Notes

  • /etc/passwd contains users registerd on the system which can perform actions and have a shell assosciated to them
  • There are 7 file types in linux
  • Log directory: /var/log
  • Types of logs: boot, chronyd, cron, maillog, secure, messages, httpd

Commands

  • scp: Command to securely transfer files between servers "scp [OPTION] [user@]SRC_HOST:]file1 [user@]DEST_HOST:]file2
  • last: lists users who had logged in earlier
  • awk: returns particular columns
  • To log a message to the syslog: logger -t error "Hey therea"
  • To run a command in the background you use nohup and &
  • In conditions, if the variable will ahve a digit or integer value we use -eq, for charachters we use ==
  • usermod -L will disable the users
  • The command used to check processes: ps -ef
  • sed command is used to perform manipulation on the data within a file that appears as output, it doesn't change the original file. For example: sed 's/lenny/gan/g' filename (this will replace lenny everywhere with gan), to change in the original file add -i flag to the command. Another example: sed -i '/^$/d' filename (Delete empty lines in the original file also)

Wild cards

      • represents zero or more charachters
  • ? - represents a single character, example: ls -l ?abcd.txt
  • [] - represents a range of characters, example: touch file[1..9].txt, ls -l [cd] //either c or d

Soft Links and Hard links

  • Inode: Pointer o number of a file on the hard disk
  • SoftLink: Link will be removed if file is removed or renamed (command: ln -s)
  • Hard Link: Deleting or renaming or moving the original file will not affect the hard link (command: ln)*

File Ownership

  • chown changes the ownership of a file
  • chgrp changes the group pwnership of a file
  • Recurrsiove ownership change -R

Combining and splitting files

  • cat file1 file2 file3 > file4
  • split file4
  • split -l 300 file.txt childfile : will split file.txt into 300 lines per file and output to childfilea, childfileab and childfileabc

Utility Commands

  • date
  • uptime
  • hostname
  • unmae
  • which
  • cal
  • bc

Terminal Commands

  • script: It stores terminal activities in a log file that can be named by a user, when a nme is not provided, the default file name typescript is used
  • exit
  • clear

Aliases

  • alias dir="ls -l | grep ^d"
  • alias tell="whoami; hostname"

NIC bonding

  • Network Interface Card bonding
  • Aggregation of multiple NIC into a single interface bond

Linux OS Hardening

  • User Account
  • User account
  • Stop Un-wanted services
  • Check on listening ports
  • Secure SSh Configuration
  • Enable SELinux
  • Change Listening services Port Numbers
  • Keep your OS up to date (Security Patches