====== Useful commands ======

===== Error investigation =====

Unfreeze PC at kernel level:\\
[[https://en.wikipedia.org/wiki/Magic_SysRq_key#Common_Usage]]\\

Show error and warning messages:\\
''# dmesg -T --level=err,warn''\\

Monitor message in real time:\\
''# dmesg -Tx --follow''\\

Test RAM:\\
''# apt-get install memtester''\\
''# memtester 1024 5''\\
(allocate 1024Mo and repeat 5 times)\\



===== Data management =====
==== File and directory size ====
''# du -sh /var/*''
==== Disk usage ====
Show disk usage with human readable values\\
''# df -h''\\
Show disk INODE usage\\
''# df -1''\\
==== Change permissions ====
Change directories permission:\\
''$ find /path/to/base/dir -type d -exec chmod 755 {} +''\\
Change files permission:\\
''$ find /path/to/base/dir -type f -exec chmod 644 {} +''\\
==== Change ownership ====
Owner:\\
''$ chown owner_name * -R''\\
Group:\\
''$ chgrp group_name * -R''\\
==== Copy / backup large folders ====
Test the command with -n\\
''$ rsync -nav --delete-after /source/ /destination/''\\
Execute command : -a for archive (keep files structure + recursive...), -v for verbose, --delete-after to delete files in backup directory if they do not exist in source (moved, renamed, ...)\\
''$ rsync -av --delete-after /source/ /destination/''\\

===== User management =====
==== Users ====
Create user:\\
''$ sudo useradd -m username''\\
Set password:\\
''$ sudo passwd username''\\


==== Groups ====
Create group:\\
''$ sudo addgroup goupname''\\
Config file:\\
''/etc/group''\\
Add user to group:\\
''$ sudo usermod -a -G groupname username''\\

===== Packages =====
List installed packages:\\
''sudo apt list --installed''\\