The installation program tries to set PasServer as a daemon, but if it fail, it's possible to set manually.
There are different alternatives to set passerver as a daemon:

• systemd service (recommended method):

Create a file inside the folder /etc/systemd/system named passerverd.service
with a content like this
[Unit]
Description=GiD password server: floating password for GiD and problemtypes
Requires=network.target
After=systemd-user-sessions.service
StartLimitIntervalSec=0
[Service]
Type=simple
ExecStart=/usr/local/passerver/passerverd -port 7073
Restart=always
RestartSec=1
[Install]
WantedBy=multi-user.target
And to enable it during startup run once
sudo systemctl enable passerverd.service
then the service can be started/stopped with
sudo systemctl start passerverd.service
sudo systemctl stop passerverd.service

• rc.local (deprecated method):

Edit the file /etc/rc.local (or /etc/rc.d/rc.local in some OS) and add a line to start passerver.
For example, if installed in /usr/local/Passerver2.5, and want to use the standard port 7073, add at the end:

1. passerverd a password server for GiD
   /usr/local/Passerver2.5/passerverd -port 7073 &
   Note 1: To edit rc.local must be root user.
   Note 2: some distributions, such as Debian, do not use rc.local for startup scripts.
   
   There are more deprecated methods, like create a script file named passerverd inside /etc/init.d and a link inside /etc/rc2.d named for example S99passerverd pointing to the script file, and the script must allow start/stop the program.