sources.list

Location: /etc/apt/sources.list

format

deb http://SITE/debian distribution component1 component2 component3
deb-src http://SITE/debian distribution component1 component2 component3

Site

• ftp.<country>.debian.org  # official mirrors (ie. ftp.hk.debian.org)
• deb.debian.org                 # not have packages itself, it provide SRV DNS record to apt-get

i.e.

[1]

deb http://ftp.debian.org/debian buster main contrib non-free

[2]

# Some packages from "proposed-updates" may also be made available via the "stable-updates" mechanism.
# updates which many users may wish to install on their systems before the next point release is made,
# such as updates to virus scanners
deb http://ftp.debian.org/debian buster-updates main contrib non-free

[3]

# http://security.debian.org/debian-security/dists/buster/updates/
deb http://security.debian.org/debian-security buster/updates main contrib non-free

[4]

deb http://ftp.debian.org/debian buster-backports main contrib non-free

deb.debian.org

dig -t SRV _http._tcp.deb.debian.org

_http._tcp.deb.debian.org. 300  IN      SRV     10 1 80 debian.map.fastlydns.net.