My current sources.list:
deb ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic main restricted universe
deb-src ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic main restricted universe
deb ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-updates main restricted universe
deb-src ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-updates main restricted universe
#deb ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-security main restricted universe
#deb-src ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-security main restricted universe
deb ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-security main restricted universe multiverse
deb-src ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-security main restricted universe multiverse
deb
Index of /ubuntu bionic partner
deb-src
Index of /ubuntu bionic partner
Original, it was:
deb ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic main restricted universe
deb-src ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic main restricted universe
deb ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-updates main restricted universe
deb-src ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-updates main restricted universe
deb ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-security main restricted universe
deb-src ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-security main restricted universe
deb ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-security main restricted universe
deb-src ftp://ftp.stratoserver.net/pub/linux/ubuntu bionic-security main restricted universe
...yes, the entries are from my provider "Strato".