error: public key is not available saat update lucid lynx

setelah sebelumnya iseng utak-atik synaptic yang akhirnya hilangnya public key. Setelah ngeluyur dengan copy and paste pesan error-nya, saya coba petunjuk yang ada di forum ubuntu. di bawah ini pesan error-nya dan cara memperbaikinya.

dikutip, hasil error saat update:

Fetched 7,493kB in 1min 41s (73.6kB/s)
Reading package lists... Done
W: GPG error: http://dl2.foss-id.web.id lucid Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5
W: GPG error: http://dl2.foss-id.web.id lucid-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5
W: GPG error: http://dl2.foss-id.web.id lucid-security Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5

Current status: 186 updates [+186], 28828 new [+28828].

perhatikan NO_PUBKEY yang tidak ada. berikut cara memperbaikinya:

ubuntu@acer-3620:~$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5

Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /etc/apt/secring.gpg --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5
gpg: requesting key 437D05B5 from hkp server keyserver.ubuntu.com
gpg: key 437D05B5: "Ubuntu Archive Automatic Signing Key " not changed
gpg: Total number processed: 1
gpg: unchanged: 1

kemudian lakukan update kembali, mudah-mudahan tidak ada error lagi