Here are some important topics you should be familiar with whenever you are managing a server.
Keep packages up to date.
All GNU/Linux distributions use package managers to easily be able to
install and update packages without manually downloading them. On
Debian, which we use here for these tutorial the package manager is
apt-get or apt for short.
It's a good idea to use apt to keep your software reasonably up to
date.
apt update
apt upgrade
Not only do up-to-date packages often come with more features, but they can also fix any possible security bugs.
Troubleshooting general problems
Often when you are installing something new, you might miss a step and run into an error, so it's important to know how to check and see what errors have happened on your computer.
On Debian and other GNU/Linux distributions that use systemd (most of
them), you can use the command journalctl to look at the system's
general log. You will probably want to run journalctl -xe as the -x
and -e as that gives the most information and starts you at the bottom
of the log to see the most recent errors.
Some programs do not use this system log, but have their own logs stored
in /var/log/, or sometimes it's more convenient to look at a specific
program's log to see only its issues.
For example, we can see that in /var/log/nginx/, nginx produces both
error and access files. The access files show you all the times
people connect to files on your server and much more. We can look at the
most recent errors by running:
tail -n 25 /var/log/nginx/error.log
The command tail -n 25 means "show me the last 25 lines of this
file." You can replace that with less to browse the whole file. In
less, navigate with arrows or vim-keys and exit with q.
systemctl
Another tool on systemd distributions is systemctl. At a basic level,
use systemctl status put-service-name-here to see if a system service
is running and its most recent log. But there's much more to
systemctl.
For example, you can run systemctl stop nginx to stop NginX and
systemctl start nginx to start it back up (or use restart for both).
When you make changes to a program's configuration files, reload well
make them reload them. If you no longer want a service to start when the
system is rebooted, use disable, or conversely, to make a service
start on reboot use enable.
Finding Files
Especially if you're new to how a GNU/Linux system is arranged, you
might need help finding files. To find program-related files, you can
just use whereis:
$ whereis nginx
nginx: /usr/sbin/nginx /usr/lib/nginx /etc/nginx /usr/share/nginx /usr/share/man/man8/nginx.8.gz
This command lists the directories related to that program. For example,
/etc/nginx is where the configuration files are and /usr/share/nginx
is where the library and module-like files are.
But whereis can be used only with installed programs. A more general
tool is the pair of updatedb and locate.
updatedb is a command that quickly indexes every file and directory on
your computer. Then you can run locate to find a file containing a
given name. After running updatedb, try running locate nginx to find
all files with "nginx" in their name.
You can make your search more specific by chaining other Unix commands
through pipes. For example, grep takes input and returns only lines
that match an extra argument. In the example below, we locate all
files with "nginx" in the name, but we use grep to only show us
those with the word "available" in them.
root@landchad:~# locate nginx | grep available
/etc/nginx/modules-available
/etc/nginx/sites-available
/etc/nginx/sites-available/default
/etc/nginx/sites-available/landchad
/usr/share/nginx/modules-available
/usr/share/nginx/modules-available/mod-http-auth-pam.conf
/usr/share/nginx/modules-available/mod-http-dav-ext.conf
/usr/share/nginx/modules-available/mod-http-echo.conf
/usr/share/nginx/modules-available/mod-http-geoip.conf
/usr/share/nginx/modules-available/mod-http-image-filter.conf
/usr/share/nginx/modules-available/mod-http-subs-filter.conf
/usr/share/nginx/modules-available/mod-http-upstream-fair.conf
/usr/share/nginx/modules-available/mod-http-xslt-filter.conf
/usr/share/nginx/modules-available/mod-mail.conf
/usr/share/nginx/modules-available/mod-stream.conf
updatedb is an ideal candidate for a cronjob so you
don't have to worry about running each time. For example, adding the
following to your crontab will run updatedb every 30 minutes:
*/30 * * * * /usr/bin/updatedb