Running portable service in systemd

Portable service is New and Preview feature added in systemd which isolates a group of services. This will just attach a subfodler or raw image that contains the OS-Tree to the host systemd. This will not provide all kind of isolation as containers does but will provide strict access control for the running service. For detailed explanation on the internals please check systemd portable service.

In this Blog will see how to create a image subfolder, populating basic hello-world application service then running that service as portable service.

Pre-requisite

Ubuntu 20.04 or higher
Portable systemd enabled. In ubuntu this can be done by installing systemd-container package.
```
 sudo apt install systemd-container
```
gcc installed. In ubuntu it can be done by following command,
```
 sudo apt install gcc
```

Creating the image sub-folder and hello world service

Portable service attach a subfolder or the raw os image to the running systemd. But the requirement is this subfolder or raw image should contain some basic folder structure (os-tree) in place. In this section we will create this structure and create a hello world service

Create the basic folder structure.

 mkdir ./portabletest
 cd ./portabletest
 mkdir -p ./usr/bin/ ./usr/lib/systemd/system/ /usr/lib/ ./etc/ ./proc/ ./sys/ ./dev/ ./run/ ./tmp/ ./var/tmp/
 cd -

Create required os files.

 touch portabletest/etc/resolv.conf
 touch portabletest/etc/machine-id
 cp /usr/lib/os-release portabletest/usr/lib/

Create a hello world application service.

 echo -e "#include <stdio.h>
 int main(void)
 {
     printf(\"hello-world\n\");
     return 0;
 }
 " > main.c && gcc -static main.c -o ./portabletest/usr/bin/helloworld

 echo -e "[Unit]
 Description=hello world

 [Service]
 Type=oneshot
 ExecStart=/usr/bin/helloworld
 RemainAfterExit=true
 StandardOutput=journal

 [Install]
 WantedBy=multi-user.target" > ./portabletest/usr/lib/systemd/system/portabletest-helloworld.service

Attaching the portable service and start

Attach the portable service.
```
 portablectl attach ./portabletest
```

Start the service and verify it is running.

 systemctl start portabletest-helloworld.service
 systemctl status portabletest-helloworld.service

Now the Portable service can be treated as any other systemd service.

Detach or remove the portable service

To detach the portable service, execute the following command,

portablectl --now detach ./portabletest

--now flag is required if this portable service contains services which is already running and you want to stop that and detach.

Pre-requisite

Creating the image sub-folder and hello world service

Attaching the portable service and start

Detach or remove the portable service

Reference