Popular Commandsps - shows the status of running processes, supports more than 80 command-line options on Linux systems. man - traditional "on-line" documentation pwd - print working directory cd - move to another directory mkdir - to make a directory rmdir - remove to directory Manuel PagesTo find out about a command: man command Manual pages are divided into different sections depending on their purpose. User commands are in section 1, Unix system calls in section 2, and so on. 1, 5 (file formats), and 8 (system administration commands). Transport Layer SecurityUses public key cryptography and PKI to secure messages between nodes on a network. TLS runs as a separate layer that wraps TCP connections. Once a client and server have established a TLS connection, the contents of the exchange, including the URL and all headers, are protected by encryption. Even More Important Directories/usr/local Programs and datafiles that have been added locally by the system administrator. /etc/skel Sample startup files you can place in home directories for new users /dev This directory contains the so-called device files, the interface between the filesystem and the hardware /proc The interface between the filesystem and the running processes, the CPU, and memory /opt Directory is often used for larger software packages More Important Directories/var/spool Temporary storage for files being printed, sent by UUCP, and so on. /usr/lib Standard libraries, such as libc.a. /usr/lib/X11 The X Window System distribution. Contains the libraries used by X clients, as well as fonts, sample resources files, and other important parts of the X package. /usr/include Standard location of include files used in C programs /usr/src Location of sources to programs built on the system. Important Directories/bin The most essential Unix commands, such as ls. /usr/bin Other commands. /sbin Very common commands used by the superuser for system administration. /usr/sbin Commands used less often by the superuser for system administration. /boot Location where the kernel and other files used during booting are sometimes stored. /etc Files used by subsystems such as networking, NFS, and mail. /var Administrative files, such as log files, used by various utilities. Boot Process TasksTasks: Finding, loading, and running bootstrapping code Finding, loading, and running the OS kernel Running startup scripts and system daemons Maintaining process hygiene and managing system state transitions Diagram of Processes Forked From Shell
Fix Key Commandsstty function key Function is what you want to do: erase, kill, intr, susp Key is the key that you press. Put () in front of key i.e C To generate list of current terminal settings: stty a Command to bring shell to a reason and making it operate as expected if it doesn't: stty sane Useful KeysCtrl-U : Delete the line from the cursor to the beginning of the line. Ctrl-C : Aborts execution. Ctrl-Z : Suspends execution. Ctrl-S : Stops the terminal output until you press Ctrl-Q. What the test command can do
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Shells on Linuxbash - Bourne Again shell. The most commonly used shell on Linux. Command-line editing, history substitution. csh - Different interface for programming. No command-line editing, history substitution. ksh - Korn shell. Command-line editing. sh - Bourne shell. The original shell. No command-line editing. tcsh - Enhanced C shell. Command-line editing. zsh - Z shell. The newest of the shells. Command-line editing. Has very powerful completion features. Linux & Unix Boot Process
More Basic Security MeasuresRoot Kits - Programs and patches that hide important system information such as process, disk, or network activity. Packet Filtering - Passes only traffic for services that you specifically want to offer from that system. Passwords and Multifactor Authentication Vigilance Application penetration testing Copying the Current Shell
OpenSSH Essentials
To Create A Temp File w/ Random Name
Security Power ToolsNmap - Network Port Scanner Nessus - Next generation network scanner Metasploit - Penetration testing software Lynis - On-box security auditing John the Ripper - Finder of insecure passwords Bro - The programmable network intrusion detection system Snort - the popular network intrusion detection system OSSEC - Host-based intrusion detection Fail2Ban - Brute-Force attack response system Remote Loginsssh -1 accountname systemname -1 specifies the account on the remote system Another syntax with identical effects is: ssh accountname@systemname To suspend remote login: ~ followed by Ctrl-Z How Security Is CompromisedSocial Engineering Software Vulnerabilities Distributed Denial-of-Service Insider Abuse Network, system, or application configuration errors Elements of SecurityConfidentiality - Privacy of data Integrity - Authenticity of Information Availability - Must be accessible to authorized to users when they need it Basic Security MeasuresSoftware Updates Unnecessary Services - Disabling unnecessary services. Remote Event Logging Backups - Regular, tested system backups are an essential part of any site security plan. Protect your backups by limiting (and monitoring) access and by encrypting backup files. Viruses and Worms To Copy Stuff Over SSHTo copy files in the SSH suite: scp Copies a file from your local system to remote system: scp filepath accountname@systemname: DO NOT FORGET COLON Copies a file from the remote system to your own: scp accountname@systemname:filepath To copy a directory: scp -r accountname@systemname:directoryname relative path. |
Viewing Filesxemacs - editor cat - used to scan a file, rather than edit it. vi - text editor more - prints a screenful at a time and waits for you to press the spacebar before printing more. Can search for a string in the file: press the slash key (/), type the string, and press Return. less - variation of more nano - simple and low-impact starter editor Linux loginPassword: # - means you are at root level $ - means you are at the user level To set a password use the "passwd" command. Startup Files.bashrc - Startup file .bash_profile - Runs only when you log in .zshrc - .bashrc but for zsh .zprofile - .bash_profile, but for zsh .cshrc - For the C shell or tcsh .login - .bash_profile for the C shell or tcsh. .emacs - For Emacs editor .exrc - For vi editor .newsrc - For news readers .xinitrc - For X Window System .kde/share/config - Directory with configuration files for the K Desktop Environment .gnome - Directory with configuration files for the GNOME Filename Expansionls - lists files. ls text?text - lists files containing digits in a position if the difference in file names is just a digit. ls text[13]text - lists files with the digits 1 and 3 in that position. ls text[1-3]text - lists all files from 1-3 inclusive in that position. Also works with alphabetical characters [a-zA-Z] ls text*text - lists all files that match the structure including a numbers and full words between the text. Common Security Flavors for NFS Protocol
NFS Drawbacks
NFS (Network File System)
Cryptographic Hash FunctionsProperties: Entanglement: every bit of the hash value depends on every bit of the input data. On average, changing one bit of input should cause 50% of the hash bits to change. Pseudo-randomness: hash values should be indistinguishable from random data. Non reversibility: given a hash value, it should be infeasible to discover another input that generates the same hash value. Public Key InfrastructureA network of entities who trust each other to varying degrees. By following indirect chains of trust outside your personal network, you can establish that a public key is trustworthy with a reasonable degree of confidence. The Public Key Infrastructure, used to implement TLS on the web, addresses this problem by trusting a third party known as a Certificate Authority (CA) to vouch for public keys. The CA signs certificates for Alice and Bob’s public keys with its own private key. Public Key CryptographyAlice generates a pair of keys. The private key remains a secret, but the public key can be widely known. Bob similarly generates a key pair and publishes his public key. When Alice wants to send Bob a message, she encrypts it with Bob’s public key. Bob, who holds the private key, is the only one who can decrypt the message. Alice can also sign the message with her private key. Bob can use Alice’s signature and her public key to validate its authenticity. Asymmetric ciphers. Symmetric Key CryptographyAlice and Bob share a secret key that they use to encrypt and decrypt messages. They must find a way to exchange the shared secret privately. Once they both know the key, they can reuse it as long as they wish. Symmetric keys are relatively efficient in terms of CPU usage and the size of the encrypted payloads. The need to distribute the shared key in advance is a serious impediment to many use cases. Cryptographic Message PropertiesConfidentiality - messages are impossible to read for everyone except the intended recipients. Integrity - it is impossible to modify the contents without detection. Non repudiation - the authenticity of the message can be validated. |
Cheatography
https://cheatography.com
Intro To System Administration - McCool Cheat Sheet (DRAFT) by cfmccool
This is a draft cheat sheet. It is a work in progress and is not finished yet.
