Basic commands

• All the commands below are tested under Ubuntu 18.04.5 LTS

To check disk size

$ df -lh

To check specific size of directory

$ du -sh /directory
$ du -sh */ | sort -hr # sort by size

Potential disk size overflow

• If you have systemd service running and with logs, the disk space maybe used up a lot when something wrong going on the service.

• You can check the size of syslog

$ du -sh /var/log/syslog*

• If there is a very big size syslog, that means most of the disk space usage is caused by the syslog

• You can limit the size of log or rotate the log by editing rsyslog located at /etc/logrotate.d/

$ sudo nano /etc/logrotate.d/rsyslog

• Example below is to limit to size of 100k and rotate for 7 logs in total

/var/log/syslog
{
    rotate 7
    size 100k
    daily
}

• However, this is just a temporary workaround, you should check why which program is generating big size of syslog

• Restart the service

$ sudo systemctl restart rsyslog.service

• Sometimes, the error message from ROS may generate big size of log as well.

• You can check using the command

$ cd
$ du -sh .ros/log

To check saved password for Wifi

$ cd /etc/NetworkManager/system-connections
$ sudo cat <saved_network_connection>

Symlink

To create symlink

$ ln -s <path to the file/folder to be linked> <the path of the link to be created>

• -s flag means the link is soft, without -s, by default it would be hard link

To remove symlink

$ unlink <path-to-symlink>

or

$ rm <path-to-symlink>

Swap memory

Check swap memory

$ free -m

Clear swap memory

• we can cycleoff the swap memory but turn it off and on again

$ sudo swapoff -a
$ sudo swapon -a

Scan ip address of devices

Dependencies

$ sudo apt install nmap

Scan

$ sudo nmap -sn <ip_address>/24 // for example 192.168.10.0/24

Add user to dialout

$ sudo usermod -a -G dialout $USER