How to set resource limits for a service with systemd

Limit CPU, memory, and I/O usage for a systemd service using cgroup directives in the unit file.

Limit CPU, memory, and I/O usage for a systemd service using cgroup directives in the unit file.

Root or sudo access on a Linux system running systemd with cgroups v2 (default on Ubuntu 22.04+, Fedora 31+, Debian 11+).

Open a drop-in override for the service:
```
sudo systemctl edit myapp.service
```
Add resource limit directives under the [Service] section. systemd enforces these limits through Linux control groups (cgroups):
```
[Service]
MemoryMax=512M
MemoryHigh=400M
CPUQuota=50%
TasksMax=100
IOWeight=50
```
MemoryMax sets a hard memory ceiling — the kernel kills the process if it exceeds this limit. MemoryHigh sets a soft limit — systemd throttles the process before reaching MemoryMax. CPUQuota=50% limits the service to 50% of one CPU core. TasksMax limits the number of processes and threads.
Restart the service to apply the limits:
```
sudo systemctl restart myapp.service
```

systemd shows applied resource limits in the service properties:

systemctl show myapp.service | grep -E "MemoryMax|CPUQuota|TasksMax"

Monitor actual resource usage with systemd-cgtop:

systemd-cgtop