Shell

SSH

• ssh to see if ssh is installed (openssh-client is installed by default)

• ssh-keygen or ssh-keygen -t rsa generate ssh key by RSA algorithm

• cat ~/.ssh/id_rsa.pub print public key (for settings on Github)

• ssh -T [e-mail] testing

• sudo apt-get install openssh-server install server for incoming ssh connections

• ssh-copy-id username@hostname copy your ssh key to remote computer to avoid verifying password on every connection

• ssh username@ip ssh login to a remote computer with this ip and username

• ssh username@hostname if mapped this hostname to its ip in /etc/hosts file

• ssh -X username@hostname login with GUI support

• ssh -p 1234 username@hostname login via port 1234

• sudo gedit /etc/hosts modify hosts file

• sudo gedit /etc/ssh/sshd_config modify ssh server configuration

Devices and Filesystem

• sudo gparted

• ls -l /dev/ttyS0

• groups <username>

• sudo gpasswd -a <username> <groupname>

• sudo gpasswd -d <username> <groupname>

• sudo groupadd <newgroupname>

• sudo usermod -a -G <groupname> <username>

• lscpu , lsmem , lshw list CPU, memory, hardware info

• lsusb list USB devices

• lsblk list block devices, often used to check external ssd

• lspci list PCI devices

• lspci | grep VGA check GPUs

• sudo lshw -C video check GPU display details

• du -h -d 1 check file size/usage in current directory

• df -h check hard disk usage

Environment Variables

• which pip to see which pip command you are running - useful for checking environment!

• uncomment #force_color_prompt=yes in .bashrc for a colored prompt

• sudo !! where !! is for the last command

• python3 -m site show searching path for python3

• sudo python -m pip install --force-reinstall pip==8.1.1 if you inadvertently upgraded your system pip. More info can be found at this link, and this link.
• sudo ldconfig after sudo make install to refresh the cache

Date and Time

• date

• sudo systemctl stop systemd-timesyncd

• sudo systemctl start systemd-timesyncd

• timedatectl

• sudo timedatectl set-ntp false

• sudo timedatectl set-time 'YYYY-MM-DD'

• sudo timedatectl set-time 'YYYY-MM-DD HH:MM:SS'

Network

• sudo systemctl restart network-manager

• nmap -sP 192.168.0.1/24 scan ports

• nmap -A 192.168.10.112 detect OS and services

Compression

• tar -cf filename.tar file1 folder2 packed without compression

• tar -xf filename.tar create an archive by -c, extract an archive by -x

• tar -cvzf filename.tar.gz file1 folder2 compress by -z; verbose by -v

• tar -xvzf filename.tar.gz decompress

• tar -xvzf filename.tar.gz -C {path} decompress to a designated path

• sudo apt-get install zip unzip

• zip -r archive_name.zip myfolder

• unzip archive_name.zip

running in the background

• Ctrl + Z to stop the process, followed by bg to run in the background or fg to run in the foreground.

• Use command ./test.sh 1>stdout.log 2>stderr.log & and it will return a process ID.

• Processes running in the background can be monitored by top command.

apt commands to find dependencies (link)

• apt-cache showpkg <pkgname> show package info, both depends and reverse depends

• apt-cache depends ros-melodic-desktop show one-level dependencies

• apt-cache rdepends --installed ros-melodic-desktop

• sudo apt install apt-rdepends

• apt-rdepends ros-melodic-desktop | pager recursively show all dependencies

• apt-rdepends --reverse protobuf-compiler | grep ros-melodic-desktop

apt commands to locate packages

• dpkg -L <package-name>

• apt list <package-name>

• apt-cache madison

• locate <filename> find a file in database (globally)

• find <filename> find a file in local directory

vim commands

• vi -b <filename> open file in binary mode

• :%!xxd switch to hex mode

• :%!xxd -r switch back to binary mode

• :wq save and exit

terminal

• sudo update-alternatives --config x-terminal-emulator

References

• The Unix Shell
• How do I find the reverse dependency of a package?