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To add swap to a WordPress VPS, first confirm that no swap is already active, create a disk-backed file, restrict it to mode 600, format it with mkswap, enable it with swapon, and add an /etc/fstab entry so it returns after reboot. A 1 GiB swap file is a reasonable starting point for a small VPS, but the right size depends on your RAM, workload and free disk space. Swap is a slower safety buffer for short memory spikes—not a substitute for adequate RAM or for fixing a leaking plugin, oversized PHP-FPM pool or overloaded database.
What swap does for a WordPress VPS
Swap is disk-backed virtual memory. When Linux cannot keep every inactive memory page in RAM, it can move some pages to a reserved area on storage and reclaim RAM for active work. The storage device is far slower than RAM, so swap protects availability during a spike but can make a heavily swapped server sluggish.
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For WordPress, swap can give PHP-FPM, the web server and the database a little room during bursts such as traffic surges, cron jobs, backups or cache warm-ups. It does not increase CPU capacity, make slow storage faster or permanently solve sustained memory pressure. If the kernel is constantly moving pages in and out of swap, the VPS may spend more time waiting on storage and still be killed by the out-of-memory (OOM) manager.
- Use swap as a safety margin: it can reduce the chance that a brief allocation spike immediately kills a service.
- Do not treat it as extra RAM: sustained demand still requires smaller services, fewer memory-heavy plugins, better database/PHP-FPM sizing or more physical memory.
- Keep disk headroom: the swap file shares storage with WordPress core, uploads, logs, database files and backups.
Check whether swap already exists
Do not create a second file until you know the current state. Run these commands as a user with sudo access:
sudo swapon --show
free -h
df -h /swapon --show lists active swap areas. In free -h, the Swap row shows total, used and available swap in readable units. If the command produces no rows and the Swap total is 0B, no active swap is configured. df -h / confirms that the root filesystem has enough free space for the file while leaving room for normal WordPress operations.
If an existing swap area is already adequate, adding another one may add complexity without solving the underlying issue. Record its path and size before changing anything.
Choose the swap size
WordPress does not mandate a swap size. A practical starting point is 1 GiB on a small VPS, then adjust after observing real memory use. DigitalOcean’s Debian guidance describes swap equal to RAM or twice RAM as a starting heuristic and notes that more than 4 GiB is often unnecessary when swap is only a fallback. Those are heuristics, not WordPress requirements.
| Situation | Starting approach | What to verify |
|---|---|---|
| Small site with occasional spikes | 1 GiB file is a reasonable example | Free disk after creating it; whether OOM events stop |
| VPS with more RAM and bursty jobs | Consider a RAM-sized file, subject to disk capacity | Peak usage during backups, imports and cron tasks |
| Persistent memory pressure | Do not simply keep enlarging swap | PHP-FPM workers, database memory, plugins and logs; consider more RAM |
| Very limited disk | Use the smallest safety buffer that leaves operational headroom | WordPress uploads, database growth and backup space |
Swap space is reserved on disk, so a 4 GiB file consumes 4 GiB that cannot be used for other data. Size it for a temporary buffer, not for the total memory your services need during normal operation.
Create a swap file on Ubuntu or Debian
The following example creates /swapfile with 1 GiB. Replace 1G or the dd count only after checking your free space and workload.
1. Create a hole-free file
On filesystems where it produces a valid, fully allocated file, use:
sudo fallocate -l 1G /swapfileSome filesystems or kernels reject swap files containing holes (unallocated ranges that look like zeros). If swapon later reports that the file has holes, create it with dd, which writes every block:
sudo dd if=/dev/zero of=/swapfile bs=1M count=1024 status=progressThe dd command writes 1,024 blocks of 1 MiB, approximately 1 GiB. It can take longer than fallocate because it actually writes the data. Btrfs has additional restrictions around swap files; check the filesystem type and use a distribution-supported method, a supported swap partition or the documented Btrfs procedure rather than forcing a regular file.
2. Restrict access to the file
sudo chmod 600 /swapfileMode 600 allows only root to read or write the file. This matters because swapped pages can contain credentials, session data or other information that ordinary users should not be able to inspect. Verify the mode if needed with ls -l /swapfile; the permissions should show read and write access for root only.
3. Format and activate it
sudo mkswap /swapfile
sudo swapon /swapfilemkswap writes the swap signature and metadata. swapon makes the area available immediately; it does not yet make the configuration persistent across a reboot.
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sudo swapon --show
free -hYou should now see /swapfile in the listing and a non-zero Swap total in free -h. A small Used value is normal; Linux may use swap for inactive pages even when RAM is not completely full.
Make swap survive a reboot
Add this exact line to /etc/fstab:
/swapfile none swap sw 0 0You can edit the file with an editor such as sudo nano /etc/fstab. Keep the path absolute. For a regular-file source, Ubuntu’s swapon documentation expects an absolute path.
After saving, test the entry without rebooting:
sudo swapon -a
sudo swapon --showswapon -a (the same operation exposed as swapon --all) reads swap entries from /etc/fstab and enables any that are not already active. If it prints an error, fix the line before rebooting. Once the test succeeds, reboot during a maintenance window and run sudo swapon --show and free -h again to confirm that the setting persisted.
Understand and tune swappiness
Swappiness is a Linux kernel value from 0 to 100 that influences how readily the system considers swapping. Many distributions use 60 as a default, but the best value depends on the storage device, available RAM and workload. It is not a measure of how much swap is allocated or currently used.
Check the current value
cat /proc/sys/vm/swappinessTest a temporary value
sudo sysctl vm.swappiness=10This change lasts until reboot. A lower value can make Linux prefer reclaiming other cache before swapping anonymous memory, but setting it blindly can also increase allocation pressure and trigger an OOM event sooner. Observe latency, swap-in activity, available RAM and application errors under your normal traffic before making a permanent change.
Persist a value only after testing
If measurements show that a different value helps, add a single setting to /etc/sysctl.conf, for example:
vm.swappiness=10Load it with:
sudo sysctl -pThere is no universal “magic” number for WordPress. A busy database, a PHP-heavy site and a lightly used blog can behave differently even on the same VPS plan.
Swap file versus swap partition
| Characteristic | Swap file | Swap partition |
|---|---|---|
| Adding space to an existing VPS | Usually easiest; can be created without repartitioning | May require an existing unused partition or disk changes |
| Resizing | Remove and recreate, or add another file, with care | Often requires partition work and downtime |
| Filesystem requirements | Must be hole-free; Btrfs has extra restrictions | Not subject to regular-file hole rules |
| Persistence | Absolute path in /etc/fstab |
Partition device or UUID in /etc/fstab |
| Operational risk | Low when permissions and filesystem support are correct | Partitioning mistakes can affect other data |
For a typical Ubuntu or Debian WordPress VPS with free space, a swap file is the least disruptive option. A partition can be appropriate when the provider or filesystem does not support regular-file swap reliably, but creating one may require provider-specific recovery or partitioning steps not covered by this procedure.
WordPress memory limits are separate from system swap
Swap operates at the operating-system level. WordPress and PHP impose separate limits on what a request may allocate. Current WordPress requirements recommend PHP 8.3 or newer, MariaDB 10.11 or newer or MySQL 8.0 or newer, and HTTPS; Apache or Nginx is recommended. Swap is not listed as a WordPress requirement.
WordPress documentation states that the default requested PHP memory is 40 MB for a single site and 64 MB for multisite. Increasing that limit can hide the cause of a memory problem instead of fixing it. A PHP fatal error such as “Allowed memory size exhausted” can therefore remain after swap is added, depending on how PHP is configured and whether the process reaches its own limit first.
What to inspect when WordPress still runs out of memory
- PHP-FPM: review the number of workers, each worker’s memory footprint and the pool’s limits. Too many concurrent workers can exhaust RAM even when each request is within its PHP limit.
- Plugins and themes: identify extensions that allocate large arrays, process images, run imports or schedule frequent jobs. Disable or replace a confirmed memory-heavy component rather than masking it with more swap.
- Database: inspect query patterns, buffer settings and concurrent connections. A database can consume most of the VPS independently of PHP.
- Background work: check WP-Cron, queues, backups, image conversion and search indexing, especially if failures coincide with scheduled tasks.
- Capacity: if memory pressure is sustained during ordinary traffic, move to a VPS with more RAM or a managed service sized for the workload.
Monitor whether swap is helping
After activation, check the server during the traffic or job that previously caused trouble. Compare RAM available, swap used and application response times rather than judging success from a non-zero swap total alone.
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free -h
sudo swapon --showA swap area that remains mostly unused can still be useful as an emergency buffer. Conversely, rapidly rising swap use, high I/O wait, slow WordPress responses or repeated service restarts indicate that the VPS is under continuing pressure. Review kernel and service logs, including:
dmesg
journalctl -k
journalctl -u php*-fpmThe exact PHP-FPM unit name varies by distribution and PHP version, so list available units if the wildcard does not match your system. Look for OOM-killer messages, worker-limit errors, database restarts and filesystem-full errors. Swap cannot compensate for a full disk; reserve capacity for logs, uploads, database growth and backups.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshoot common failures
swapon: /swapfile has holes
The file was created with unallocated ranges that the kernel will not accept for swap. Remove and recreate it with dd:
sudo swapoff /swapfile 2>/dev/null || true
sudo rm -f /swapfile
sudo dd if=/dev/zero of=/swapfile bs=1M count=1024 status=progress
sudo chmod 600 /swapfile
sudo mkswap /swapfile
sudo swapon /swapfileDo not run the removal sequence if /swapfile is an existing, valuable configuration you have not backed up; confirm the path first. The Ubuntu swapon manual documents the hole restriction.
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Invalid argument or a Btrfs-related error
Check the filesystem that contains the file:
findmnt -no FSTYPE,TARGET /On Btrfs, regular swap files have additional requirements and restrictions. Use the distribution’s documented Btrfs method, a supported swap partition or another filesystem approved by your provider. Do not assume that a command that works on ext4 is valid on Btrfs.
Swap disappears after reboot
Inspect /etc/fstab for the exact line /swapfile none swap sw 0 0, then test it:
sudo swapon -a
sudo swapon --showCommon causes include a typo in the path, a missing swap type, an extra character in the file or a failed activation that was not noticed before reboot. Read the error printed by swapon -a and check the kernel log.
The VPS still OOMs
More swap may only postpone failure. Inspect dmesg, service logs, PHP-FPM worker counts, database usage and plugin behavior. If the machine reaches its physical and swap limits during normal operation, reduce concurrent work, fix the memory consumer or add RAM. Also verify that the disk is not full and that the provider has not imposed a storage or I/O limit.
mkswap or swapon reports permission problems
Run administrative commands with sudo, confirm that /swapfile is owned by root and has mode 600, and check that no existing mount or file occupies the path. A file on a read-only filesystem cannot be formatted or enabled.
Removing or replacing a swap file
If you need to replace the file, disable it first and remove its persistent entry:
sudo swapoff /swapfile
sudo rm /swapfileThen delete the corresponding /swapfile none swap sw 0 0 line from /etc/fstab. Verify with sudo swapon --show and free -h. Never delete an active swap file before running swapoff; processes may depend on pages currently stored there. Ensure that the system has enough free RAM before disabling it, particularly on a busy production site.
Quick Recap
A safe operating checklist
- Confirm current swap with
sudo swapon --showandfree -h. - Check free space with
df -h /and leave room for WordPress data, logs, databases and backups. - Choose a temporary-buffer size based on RAM and observed peaks; 1 GiB is only an example.
- Create a hole-free file; use
ddiffallocateproduces a hole-related failure. - Set mode 600 before enabling the file.
- Run
mkswap,swaponand both verification commands. - Add the exact absolute path to
/etc/fstaband test withsudo swapon -a. - Change swappiness only after observing the workload; test temporary values first.
- Investigate PHP, database, plugin and worker behavior when OOM events persist.
- Use more RAM or a managed WordPress/Linux service when memory demand is consistently above the VPS’s capacity.
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