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

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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