Check whether you have any

free -h
swapon --show

If Swap: shows 0B and swapon --show prints nothing, there is none.

Create a swap file

Size guidance: equal to RAM for servers up to 4 GB; half of RAM above that; 2 GB is enough on most web servers regardless. Here, 2 GB:

sudo fallocate -l 2G /swapfile
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfile

chmod 600 matters: swap can contain fragments of anything that was in memory, including passwords. If fallocate is unavailable on your filesystem, dd does the same job more slowly:

sudo dd if=/dev/zero of=/swapfile bs=1M count=2048 status=progress

Verify:

free -h

Make it permanent

The swap file is active now but forgotten at reboot. Add it to /etc/fstab:

echo '/swapfile none swap sw 0 0' | sudo tee -a /etc/fstab

Test the line without rebooting: sudo swapoff /swapfile && sudo swapon -a && free -h.

Set swappiness

Swappiness (0–100) is how eagerly the kernel moves pages to swap. The default of 60 is tuned for desktops and makes a server swap out application memory while there is still RAM free, which is slow. For a web server, 10 is right: swap is used only under real pressure.

sudo sysctl vm.swappiness=10
echo 'vm.swappiness=10' | sudo tee /etc/sysctl.d/99-swappiness.conf

A related knob, vm.vfs_cache_pressure=50, makes the kernel hold on to directory and file metadata longer — helpful for PHP applications that stat thousands of files per request.

What swap is not

It is not more RAM. Swap on NVMe is still a hundred times slower than memory; a server that is constantly swapping is a server that needs more RAM or a lighter workload. Check whether that is you:

vmstat 1 5

Look at the si and so columns (swap in/out per second). Occasional small numbers are fine. Sustained hundreds or thousands mean memory is genuinely short. Find the hungry processes:

ps aux --sort=-%mem | head -8

On a PHP server the fix is usually fewer PHP-FPM workers (tuning PHP-FPM pools) or a smaller MySQL buffer pool; on a small VPS it is the next plan up.

Removing or resizing

sudo swapoff /swapfile
sudo rm /swapfile
# then recreate at the new size, and update /etc/fstab if the path changed

zram: the alternative on small VPSs

On a 1 GB server, compressing memory in RAM (zram) can be better than swapping to disk. Ubuntu: sudo apt install zram-tools, then set PERCENT=50 in /etc/default/zramswap. It gives roughly 1.5–2× effective memory for the pages that compress well, at some CPU cost.

VPSPioneer managed VPS plans are provisioned with swap and swappiness set as above, and memory is one of the metrics we alert on — a server that starts swapping heavily gets a ticket from us suggesting what to change before it becomes an outage.

Originally published at vpspioneer.com. More guides on hosting, Linux and servers: vpspioneer.com/blog.

Where domains live on disk

Every domain in an account has its own directory tree under the account's home:

/home/<user>/domains/example.com/
    public_html/      the web root, what visitors see
    private_html/     historically the HTTPS root
    logs/             Apache access and error logs
    stats/            web statistics

public_html is where index.php goes. private_html is a leftover from the days when the HTTPS site could be different from the HTTP one; on any current install it is a symlink to public_html, so both protocols serve the same files. If you ever find a domain serving different content over HTTPS, check whether private_html has become a real directory, and use the Use a symbolic link from private_html to public_html setting on the domain in Domain Setup to put it back.

The Apache error log for a domain is also mirrored at /var/log/httpd/domains/example.com.error.log on AlmaLinux and Rocky, or under /var/log/apache2/domains/ on Debian and Ubuntu, which is where the admin looks.

Add a second domain

User Level → Account Manager → Domain Setup → Add New. Type the domain name, and set whether it may use its own share of the account's bandwidth and disk (the default is to share the account's limits), and whether SSL, CGI and PHP are on for it. Save, and DirectAdmin creates the directory tree above, a DNS zone in /var/named/example.com.db, the mail domain and the Apache virtual host. It is live once the task queue runs, usually within the minute.

Two things to check on the DNS side. If this server runs the domain's nameservers, the zone it just created is complete and you only need to point the domain at those nameservers at the registrar. If DNS is elsewhere, at Cloudflare or the registrar, add an A record there for example.com and www pointing at the account's IP, and the zone on this server is ignored.

A domain can only exist once on a server. If another account already has it, even as a pointer, the add fails with a message saying so, and the admin has to remove it from the other account first. Once the domain is added, the SSL page issues its certificate.

Add a subdomain

Account Manager → Subdomain Management, pick the parent domain, type the subdomain name and add. The document root defaults to a directory inside the parent's web root:

/home/<user>/domains/example.com/public_html/blog/

That works, but it has a side effect: example.com/blog/ and blog.example.com serve the same files, and if the parent site is WordPress its .htaccess rules can catch requests meant for the subdomain. Recent versions let you set a different document root when creating the subdomain; putting it outside the parent's public_html avoids the overlap.

DirectAdmin adds the subdomain's A record to the zone automatically. Subdomains do not get their own mail; mail@blog.example.com is not something the panel creates.

Add a domain pointer

Account Manager → Domain Pointers. A pointer is a second name for an existing domain, and the form offers two kinds.

An alias pointer serves the same site under both names. example.co.uk shows exactly what example.com shows, with the address unchanged in the browser, and mail to @example.co.uk is delivered to the same mailboxes. Aliases are added to the domain's Let's Encrypt certificate automatically the next time it is issued, so both names work over HTTPS.

A redirect pointer sends a visitor to the main domain with a 301, so example.co.uk becomes example.com in the browser. This is the right choice for a domain you are retiring in favour of a new one, or when you want one canonical name for search engines and only bought the other domain to stop someone else using it.

Domain, subdomain or pointer

The rule we use: if the name gets its own site, its own files and probably its own mailboxes, it is a domain. If it is a section of an existing site with a name of its own, shop., app., staging., it is a subdomain. If it should show a site that already exists, it is a pointer. Domains and pointers count against separate limits in the package, so a customer who adds every spare domain as a full domain may hit their domain limit while pointers go unused.

Wildcards

A wildcard, *.example.com, is not a checkbox on any of these pages. It starts in DNS Management with an A record for *, so every unknown subdomain resolves to the server. What then answers depends on Apache: DirectAdmin does not create a wildcard virtual host by itself, so the admin adds one for the domain under Admin Level → Server Manager → Custom HTTPD Configurations. The certificate side is simpler, since DirectAdmin can issue a wildcard Let's Encrypt certificate when it hosts the domain's DNS, and 1.709 made that check faster.

Test before DNS moves

When a domain is being moved from another host, add it in DirectAdmin first and test it before changing DNS by putting a line in your own computer's hosts file that maps example.com and www.example.com to the server's IP. When it looks right, change the nameservers or A records; when they have propagated, request the certificate. On VPSPioneer free migrations this is exactly the order we work in.

Originally published at vpspioneer.com. More guides on hosting, Linux and servers: vpspioneer.com/blog.

Finding your way around

pwd, ls, cd — where am I, what is here, go there.

ls -lah            # long format, hidden files, human sizes
cd -               # back to the previous directory

find — locate files by name, size, age or owner.

find /var/www -name "*.log" -size +100M
find . -mtime -1                   # changed in the last 24 hours
find . -user root -type f          # files root created in the web tree

Reading files and logs

cat, less, tail, head — show a file, page through it, show the end or the start.

tail -f /var/log/nginx/error.log        # follow live
tail -n 200 /var/log/syslog | less      # last 200 lines, paged

grep — search text. The single most useful command on the list.

grep -i "error" /var/log/php-fpm.log
grep -rn "DB_PASSWORD" /var/www/         # recursive, with line numbers
grep -v "200 " access.log | tail         # everything that is not a 200

Resources and what is running

top / htop — live view of CPU, memory and processes. Press M to sort by memory, P by CPU, q to quit.

free -m — memory in megabytes. Look at available, not free; Linux uses spare RAM as cache and gives it back.

df -h and du -sh — disk usage per filesystem, and size of a directory.

df -h
du -sh /var/www/* | sort -h | tail       # biggest sites last

ps — list processes.

ps aux --sort=-%mem | head              # hungriest by memory
ps aux | grep php-fpm | wc -l           # how many PHP workers

ss — what is listening on which port (replaces netstat).

sudo ss -tulpn

Services

systemctl — start, stop, restart, enable, and see status.

sudo systemctl restart nginx
sudo systemctl status mariadb
sudo systemctl enable --now redis

journalctl — logs for anything systemd runs.

sudo journalctl -u nginx -n 100 --no-pager
sudo journalctl -p err -b                # all errors since boot

Moving things

cp, mv, rm, mkdir — copy, move/rename, delete, create directory.

cp -a site/ site-backup-$(date +%F)/    # -a keeps permissions and timestamps
rm -rf cache/*                          # careful: no undo
mkdir -p a/b/c                          # create the whole path

rsync — copy that only transfers changes, local or over SSH.

rsync -avz --delete /var/www/ user@backup:/srv/www/

scp — copy a single file over SSH.

scp backup.sql.gz user@203.0.113.10:/tmp/

tar — archive and compress.

tar -czf site-$(date +%F).tar.gz /var/www/example.com
tar -xzf site-2026-09-15.tar.gz

Permissions and users

chmod, chown — mode and owner. Full guide: Linux file permissions explained.

sudo — run one command as root. sudo -i opens a root shell; sudo -u www-data php artisan … runs as another user.

Network

curl — fetch a URL, see headers, test an API.

curl -I https://example.com               # headers only
curl -s -o /dev/null -w "%{http_code} %{time_total}s\n" https://example.com

dig — DNS lookups. dig example.com A +short, dig example.com MX.

ping and traceroute / mtr — is it reachable, and where does the path slow down.

Text editing

nano — the editor that does what you expect. Ctrl+O save, Ctrl+X exit. Use vim if you already know it; do not learn it on a production server at 2 a.m.

The habits that matter more than the commands

• Press Tab to complete file names; you will make fewer typos.

• history | grep finds the command you ran last month.

• Before rm -rf, run ls on the same path first.

• Read the whole error message. The answer is almost always in it.

Every one of these works on any VPSPioneer managed VPS and on shared plans with SSH enabled. If a command's output does not make sense, paste it into a ticket — that is the fastest way we can help.

Originally published at vpspioneer.com. More guides on hosting, Linux and servers: vpspioneer.com/blog.