Linux Checklist

Linux Beginner

File System Hierarchy

• / (aka root)
• /bin and /sbin
• /opt
• /usr
• /var
• /home
• /etc
• /proc

• /tmp

• Test
  • What is ‘/’?
  • What is stored in ‘/bin’? what about /etc?
  • What ‘/home’ is usually used for?
  • What type of files can you find in ‘/var’?
  • What is unique about /tmp?

Navigation

• Commands
  • pwd - where am I?
  • cd - change directory

• relative vs. absolute paths

• Test
  • How to check your current path?
  • Where cd .. will take you?
  • What would be the effect of running cd .?
  • What will happen when running ‘cd -‘?

Files

• Types of files
  • Regular
  • Directory
  • Socket
  • Character Device
  • Block Device
  • Link
  • Named Pipe
• Commands
  • ls - list files and directories
    • -a for listing hidden files
    • -l for list formt
    • -t order by time
    • -F better distinguish between regular files and directories
  • touch - creating files (original intention is updating timestamp)
    • nice to know: touch file{1..5}
  • rm - remove files
    • -r for recursive
    • -f to force removal, no questions asked
  • mkdir - create directories
    • -p - for creating multiple nested directories
  • rmdir - remove directories
  • cat - concatenate files (common usage: read a file)
  • mv - move files directories (also rename files and directories)
  • cp - copy a file
    • -r for recursive (copy a directory)
  • less - display files on a page-by-page basis
• Test
  • How to list hidden files?
  • How to create an empty new file?
  • How to remove a directory?
  • How to rename a file?
  • How to copy an entire directory with all its files?

Pattern Matching

This also known as File Globbing

• Patterns
  • * - matches zero or more of any character
  • ? - matches one of any character

Commands

• man - manual for commands
• which - get full path for given command
• whatis - one-line manual page descriptions
• whereis - locate the binary, source, and manual page files for a command
• history - command history list
  • use ![number line] to execute a command from the list

Shell & Terminal

• Terminal
  • clear - clear the terminal screen (ctrl+l can be also used)
  • ctrl+r- history search of commands
  • exit (or logout) - terminate a process, quit the shell
• Shell
  • env - see your environment variables
    • $HOMR - your home directory
    • $USER - your username
    • $PATH - list of paths where your OS searches for commands you run
  • echo - display a line of text
  • alias - define or display command shortcuts/aliases

Distributions

• Popular distributions
  • Fedora
  • Ubuntu
  • RHEL, CentOS
  • Mint
  • Debian
  • Arch Linux
  • openSUSE
• Test
  • What is a distribution?

I/O redirection and manipulation

• File Descriptor
  • stdin 0 (standard input) <
  • stdout 1 (standard output) >
  • stderr 2 (standard error) 2>

• Append »

• Pipe
  • For example: cat file | wc -l to count number of lines
• Commands
  • ‘tr’ - translating characters
    • echo "hello" | tr h H for example
  • tee - writing output to two different streams
• Test
  • How to redirect output?
  • What would be the result of the following command blop 2> file?

Text Editor

Learning how to use one of them is more than enough

• vim
  • i to start typing
  • :wq to exit (or shit+zz)
• nano
• emacs
• atom

• sublime

• Test (mainly for vim)
  • How to remove an entire line?
  • How to copy 5 lines?
  • How to jump to the end of the line
  • How to remove one word
  • How to jump to the end of the file

Users

• Types of users
  • regular
  • root
• Commands
  • useradd - add users
  • usermod - modify users
  • userdel - delete users
  • who - show who is logged on
  • passwd - changing password
  • lastlog - recent login of users
  • su - substitute users (in other words, switch to another user)
• Files
  • /etc/passwd - stores users information
  • /etc/shadow - hashed passwords
  • /etc/group - group
• Test
  • how to add a new user?
  • should you be using your user or root?

Permissions

• File Permissions
  • r for readable (2^2=4)
  • w for writeable (2^1=2)
  • x for executable (2^0=1)
• Commands
  • chmod - modify permissions
    • chmod u+x file - grant execute permissions to owner of the file
    • chmod +x file - grant execute permissions to everyone
    • chmod 444 file - grant read permissions to everyone
    • chmod 600 file - grant read and write permissions to owner of the file
  • chown - change user ownership of the file
  • chgrp - change group ownership of the file
  • umask - get or set file mode creation mask (default permissions in simpler words)
• SUID (Set User ID) - allow users running a program as the user owner
  • sudo chmod u+s file
  • sudo chmod 4755 file
• SGID (Set Group ID) - allow users running a program as the group owner
  • sudo chmod g+s file
  • sudo chmod 2555 file
• sudo
  • sudo command
  • /etc/sudoers file
• Sticky Bit - only root or owner can modify and/or delete files
  • It’s set on /tmp
  • sudo chmod +t directory
  • sudo chmod 1755 directory

Linux Intermediate

Linux Network

• Commands
  • ping - test the reachability of a host
    • -c for number of packets
  • ip - manage routing, network devices, interfaces and tunnels
    • ip a for interfaces
    • ip r for routing
    • ip neigh for any ARP related operation
  • ethtool - query and manipulate driver and hardware settings
    • -p for interface led blinking
    • -t for running tests to check your network interface
    • -S for getting statistics
  • arp- manipulate the system ARP cache
  • dhclient- DHCP client
  • netstat - display network connections
    • -n for IP addresses instead of hostnames
    • -t to show only TCP connections
    • -p to show the PID of the program
    • -l to show only listening sockets
  • lsof - list open files
    • -i for sockets
  • traceroute - print the route packets trace to network host
  • mtr - network diagnostic tool (traceroute + ping)
• Files
  • /proc/net/dev - network interfaces list
  • /pro/net/arp - ARP table
  • /etc/sysconfig/network-scripts/* - network configuration files in RHEL based OSs
  • /etc/network/interfaces - network configuration files in Ubuntu
• Types of interfaces
  • Regular
  • Dummy
  • Virtual IP
  • Veth
• Bonding
  • Modes
  • How to activate
• Network Namespaces
  • ip netns
    • ip netns add for adding namespaces
    • ip netns list for listing namespaces
    • ip netns del for removing namespaces
    • ip netns exec for executing commands inside a network namespace
• Network Kernel Parameters
  • sysctl net.*
  • /proc/sys/net/*
• Packet Sniffers (one is enough)
  • tcpdump
  • wireshark
  • dhcpdump
  • httpry
• Test
  • How to list the interfaces in your system?
  • How to display the routing table?
  • How to change the MTU of an interface?

Debugging & Troubleshooting

• CPU and Memory
  • top - processes memory and cpu consumption
  • free - amount of free and used memory
    • -g for the amount of memory in gigabytes
  • vmstat - virtual memory statistics
  • htop - interactive process viewer
  • atop - system and process monitor
  • /proc/meminfo
• Network Commands
  • netstat - network connections
  • traceroute - network connections
  • IPTraf - IP LAN monitoring
  • iftop - network bandwidth monitoring
• Disk and Filesystem
  • iotop - I/O monitor
  • iostat - I/O statistics for devices and partitions

Processes

• States
  • Running
  • Waiting
  • Stopped
  • Zombie
• Commands
  • ps - process status
  • kill [pid] - terminate processes
  • pkill - terminate processes based on names and other attributions
• Files
  • /proc/[PID]
• Running in the background
  • For example: my_program &
• Signals
  • Types
    • SIGTERM - default signal to terminate a process gracefully
    • SIGKILL - terminate process “brutally” (kill -9)
    • SIGHUP - mostly used for reloading configuration of a process/service
  • Commands
    • trap - “catch” a signal

Archives

• Commands
  • tar
  • gzip
  • zip
  • unzip
• Test
  • How to create an archive?
  • How to extract the content of an archive?

Files & Output - Intermediate level

• Commands
  • find - search for files
  • sort - sort, merge, or sequence check text files
  • wc - count lines, words, …
  • grep - search files for characters that match a certain pattern
    • -R for recursive search in all files under a certain directory
    • -i for ignoring case sensitive
  • nl - line numbering
  • uniq - remove duplicates
  • join - join multiple files together
  • split - split one file into multiple different files

Storage & Filesystem

• inode

• Links
  • soft link
  • hard link
• Commands
  • file - determine file type
  • stat - file or file system status
  • du - file space usage
  • df - disk usage of the file system
  • mount - mount filesystems
• LVM
  • pv
  • vg
  • lv
• Test
  • Can you create soft links between different file systems? what about hard links?
  • What information inode stores?

Linux Advanced

Hardware

• Commands
  • lshw - list hardware
  • lspci - list all PCI devices
  • dmidecode - DMI table decoder

System Calls

• open
• read
• exec
• clone
• fork
• vfork