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# FIX MISSING GPG KEY FOR APT-GET #
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# When running "apt-get update" If get error like this:
# W: GPG error: http://ftp.us.debian.org squeeze-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8B48AD6246925553

# basically this line was failing due to missing key in my source.list file
deb http://ftp.us.debian.org/debian/ squeeze-updates main

# Remember when you run apt-get update, /etc/apt/sources.list and anything in /etc/apt/sources.d gets processed for repos, repos require keys for authentication

# what is missing is the archive.key to authenticate that repo server is legit
# looking at this line "deb http://ftp.us.debian.org/debian/ squeeze-updates main"
# we can go here http://ftp.us.debian.org/debian/
# and look for "archive.key" then "wget link" and "apt-get add file.key" (like manual method 1)
# sometimes the key file will not be there and will be on gpg servers (method 2 and automatic method at the bottom)

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# MANUAL SOLUTION 1 #
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# Find the key link (if you know which one you need)

wget <gpg key url> 
apt-get add <keyfile that was downloaded>

##############
# KEY SERVER #
##############

# for next methods we will get the key from these gpg servers that  hold keys

# Works for debian: pgpkeys.mit.edu
# Works for ubuntu: subkeys.pgp.net

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# MANUAL SOLUTION 2 #
#####################

# If you dont know which one you want, then you need to look for it using its key id

# Example:
# We see key ID is 8B48AD6246925553

# Basically do a google Search for that key
# 8B48AD6246925553

# Google search for me return pgpkeys.mit.edu as possible match

# Find which keyservers have it, like in this case

gpg --keyserver pgpkeys.mit.edu --recv 8B48AD6246925553

# SIDENOTE, to see the key that just got stored into the gpg cache: gpg --export --armor 8B48AD6246925553

gpg --export --armor 8B48AD6246925553 > missingkey.gpg
apt-key add missingkey.gpg

# OR IN ONE COMMAND YOU CAN DO BOTH: gpg --export --armor 8B48AD6246925553 | apt-key add -

# That will download the key from the gpg cache

# SIDE NOTE: see current keys:
gpg --list-keys

# NOTE: even though gpg cache has the key, you still need to tell apt to use it, so thats why we "export" it and then import/add it into apt

####################
# Run this script: #
####################

apt-get update 2> /tmp/keymissing; for key in $(grep "NO_PUBKEY" /tmp/keymissing |sed "s/.*NO_PUBKEY //"); do echo -e "\nProcessing key: $key"; gpg --keyserver pgpkeys.mit.edu --recv $key && gpg --export --armor $key | apt-key add -; done

# it works if the command finished and says things like:
#  gpg: requesting key 46925553 from hkp server pgpkeys.mit.edu
#  gpg: key 46925553: "Debian Archive Automatic Signing Key (7.0/wheezy)
#  <ftpmaster@debian.org>" not changed
#  gpg: Total number processed: 1
#  gpg:              unchanged: 1

# If doesnt work and stuck on 
# gpg: requesting key 46925553 from hkp server pgpkeys.mit.edu

# Then copy key from this line
# "Processing key: 8B48AD6246925553"
# and google search "8B48AD6246925553" this will return keyserver, like below, put those in for --keyserver line

# And look for keyserver

# Works for debian: pgpkeys.mit.edu
# Works for ubuntu: subkeys.pgp.net