mjhjmtu

Clean install of SMP Debian 4.9.30-2+deb9u2 (2017-06-26) x86_64 GNU/Linux on an HP G62-144DX with 4G of memory, 500G HD and Intel® Core™ i3 CPU M 330 @ 2.13GHz × 4
Everything working fine. I had updated the apt repository a couple of times to make sure there were no updates so I know it was working before I tried to add non-free.

After choosing "DFSG-compatible Softeare with Non-Free Dependencies (contrib)" in synaptic apt became "unhappy." I have tried looking for answers but am either in the wrong places or it's just me (i.e. Murphy's law).

When apt-get update is called I get the following:

# apt update
Ign:1 http://ftp.us.debian.org/debian stretch InRelease
Hit:2 http://ftp.us.debian.org/debian stretch-updates InRelease
Hit:3 http://ftp.us.debian.org/debian stretch Release 
Err:2 http://ftp.us.debian.org/debian stretch-updates InRelease 
 The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010
Hit:4 http://security.debian.org/debian-security stretch/updates InRelease 
Err:5 http://ftp.us.debian.org/debian stretch Release.gpg 
 The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010 NO_PUBKEY CBF8D6FD518E17E1 NO_PUBKEY EF0F382A1A7B6500
Err:4 http://security.debian.org/debian-security stretch/updates InRelease
 The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9D6D8F6BC857C906 NO_PUBKEY 8B48AD6246925553
Reading package lists... Done
Building dependency tree 
Reading state information... Done
All packages are up to date.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://ftp.us.debian.org/debian stretch-updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://ftp.us.debian.org/debian stretch Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010 NO_PUBKEY CBF8D6FD518E17E1 NO_PUBKEY EF0F382A1A7B6500
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://security.debian.org/debian-security stretch/updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9D6D8F6BC857C906 NO_PUBKEY 8B48AD6246925553
W: Failed to fetch http://security.debian.org/debian-security/dists/stretch/updates/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9D6D8F6BC857C906 NO_PUBKEY 8B48AD6246925553
W: Failed to fetch http://ftp.us.debian.org/debian/dists/stretch-updates/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010
W: Failed to fetch http://ftp.us.debian.org/debian/dists/stretch/Release.gpg The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY 7638D0442B90D010 NO_PUBKEY CBF8D6FD518E17E1 NO_PUBKEY EF0F382A1A7B6500
W: Some index files failed to download. They have been ignored, or old ones used instead.

I tried going back by unchecking the option in Synaptic and by copying sources.list.saved to sources.list with no luck.

As far as I can tell apt-key has all the keys that update is griping about. Here are the relavent outputs I can think of:

Sources.list after the fall:

# 

# deb cdrom:[Debian GNU/Linux 9.0.0 _Stretch_ - Official amd64 NETINST 20170617-13:06]/ stretch main

# deb cdrom:[Debian GNU/Linux 9.0.0 _Stretch_ - Official amd64 NETINST 20170617-13:06]/ stretch main

deb http://ftp.us.debian.org/debian/ stretch main contrib
deb-src http://ftp.us.debian.org/debian/ stretch main contrib

deb http://security.debian.org/debian-security stretch/updates main contrib
deb-src http://security.debian.org/debian-security stretch/updates main contrib

# stretch-updates, previously known as 'volatile'
deb http://ftp.us.debian.org/debian/ stretch-updates main contrib
deb-src http://ftp.us.debian.org/debian/ stretch-updates main contrib

apt-key list:

# apt-key list
/etc/apt/trusted.gpg.d/debian-archive-jessie-automatic.gpg
----------------------------------------------------------
pub rsa4096 2014-11-21 [SC] [expires: 2022-11-19]
 126C 0D24 BD8A 2942 CC7D F8AC 7638 D044 2B90 D010
uid [ unknown] Debian Archive Automatic Signing Key (8/jessie) <ftpmaster@debian.org>

/etc/apt/trusted.gpg.d/debian-archive-jessie-security-automatic.gpg
-------------------------------------------------------------------
pub rsa4096 2014-11-21 [SC] [expires: 2022-11-19]
 D211 6914 1CEC D440 F2EB 8DDA 9D6D 8F6B C857 C906
uid [ unknown] Debian Security Archive Automatic Signing Key (8/jessie) <ftpmaster@debian.org>

/etc/apt/trusted.gpg.d/debian-archive-jessie-stable.gpg
-------------------------------------------------------
pub rsa4096 2013-08-17 [SC] [expires: 2021-08-15]
 75DD C3C4 A499 F1A1 8CB5 F3C8 CBF8 D6FD 518E 17E1
uid [ unknown] Jessie Stable Release Key <debian-release@lists.debian.org>

/etc/apt/trusted.gpg.d/debian-archive-stretch-automatic.gpg
-----------------------------------------------------------
pub rsa4096 2017-05-22 [SC] [expires: 2025-05-20]
 E1CF 20DD FFE4 B89E 8026 58F1 E0B1 1894 F66A EC98
uid [ unknown] Debian Archive Automatic Signing Key (9/stretch) <ftpmaster@debian.org>
sub rsa4096 2017-05-22 [S] [expires: 2025-05-20]

/etc/apt/trusted.gpg.d/debian-archive-stretch-security-automatic.gpg
--------------------------------------------------------------------
pub rsa4096 2017-05-22 [SC] [expires: 2025-05-20]
 6ED6 F5CB 5FA6 FB2F 460A E88E EDA0 D238 8AE2 2BA9
uid [ unknown] Debian Security Archive Automatic Signing Key (9/stretch) <ftpmaster@debian.org>
sub rsa4096 2017-05-22 [S] [expires: 2025-05-20]

/etc/apt/trusted.gpg.d/debian-archive-stretch-stable.gpg
--------------------------------------------------------
pub rsa4096 2017-05-20 [SC] [expires: 2025-05-18]
 067E 3C45 6BAE 240A CEE8 8F6F EF0F 382A 1A7B 6500
uid [ unknown] Debian Stable Release Key (9/stretch) <debian-release@lists.debian.org>

/etc/apt/trusted.gpg.d/debian-archive-wheezy-automatic.gpg
----------------------------------------------------------
pub rsa4096 2012-04-27 [SC] [expires: 2020-04-25]
 A1BD 8E9D 78F7 FE5C 3E65 D8AF 8B48 AD62 4692 5553
uid [ unknown] Debian Archive Automatic Signing Key (7.0/wheezy) <ftpmaster@debian.org>

/etc/apt/trusted.gpg.d/debian-archive-wheezy-stable.gpg
-------------------------------------------------------
pub rsa4096 2012-05-08 [SC] [expires: 2019-05-07]
 ED6D 6527 1AAC F0FF 15D1 2303 6FB2 A1C2 65FF B764
uid [ unknown] Wheezy Stable Release Key <debian-release@lists.debian.org>

So if I am reading this right apt has all the keys it needs to recognize the distro but refuses to do so.

Can someone tell me what I am missing? I have little hair left and ripping it out a handful at a time has not helped either to answer the question or to improve my appearance.

Added df -h per request

$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 0 1.9G 0% /dev
tmpfs 376M 6.2M 370M 2% /run
/dev/sda1 92G 6.8G 80G 8% /
tmpfs 1.9G 12K 1.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
/dev/sda6 19G 3.1G 15G 18% /home
/dev/sda7 341G 82G 242G 26% /store
tmpfs 376M 16K 376M 1% /run/user/119
tmpfs 376M 44K 376M 1% /run/user/1000
/dev/sdb2 1008G 71G 887G 8% /media/mhenwood/1T Files
/dev/sdb3 839G 68G 771G 9% /media/mhenwood/MS_STORE
/dev/sr0 11M 11M 0 100% /media/cdrom0

Are you looking for anything besides a full disk? - just curious

Same issue on my brand new debian 9 installed with the release installer.
The issue disappeared after getting the trusted.gpg file out of the way :

sudo mv trusted.gpg trusted.gpg-broken

Afterwards apt seems to be happy. So am I !