Add user with useradd command

based on https://unix.stackexchange.com/questions/28526/add-a-user-to-the-system-only-if-it-doesnt-exist

contrib/deb/generate.sh

@@ -39,11 +39,6 @@ mkdir -p /tmp/$PKGNAME/
 mkdir -p /tmp/$PKGNAME/debian/
 mkdir -p /tmp/$PKGNAME/usr/bin/
 mkdir -p /tmp/$PKGNAME/etc/systemd/system/
-mkdir -p /tmp/$PKGNAME/usr/lib/sysusers.d/
-
-cat > /tmp/$PKGNAME/usr/lib/sysusers.d/alfis.sysusers << EOF
-u alfis - "alfis user"
-EOF
 
 cat > /tmp/$PKGNAME/debian/changelog << EOF
 Please see https://github.com/Revertron/Alfis/
@@ -77,6 +72,8 @@ EOF
 cat > /tmp/$PKGNAME/debian/postinst << EOF
 #!/bin/sh
 
+id -u somename &>/dev/null || useradd --system alfis || echo "Failed to create user 'alfis' - please create it manually and reinstall"
+
 if ! getent group alfis 2>&1 > /dev/null; then
   groupadd --system --force alfis || echo "Failed to create group 'alfis' - please create it manually and reinstall"
 fi