I am new to Linux. I have installed Ubuntu 24.04. when I try to update the repository. this happens
Get:1 http://security.ubuntu.com/ubuntu noble-security InRelease [126 kB]
Err:1 http://security.ubuntu.com/ubuntu noble-security InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 871920D1991BC93C
Hit:2 https://dl.google.com/linux/chrome/deb stable InRelease
Hit:3 http://in.archive.ubuntu.com/ubuntu noble InRelease
Hit:4 https://ppa.launchpadcontent.net/kicad/kicad-8.0-releases/ubuntu noble InRelease
Get:5 http://in.archive.ubuntu.com/ubuntu noble-updates InRelease [126 kB]
Ign:6 https://ppa.launchpadcontent.net/octave/stable/ubuntu noble InRelease
Err:7 https://ppa.launchpadcontent.net/octave/stable/ubuntu noble Release
404 Not Found [IP: 2620:2d:4000:1::81 443]
Hit:8 http://in.archive.ubuntu.com/ubuntu noble-backports InRelease
Get:9 http://in.archive.ubuntu.com/ubuntu noble-updates/main amd64 Packages [468 kB]
Get:10 http://in.archive.ubuntu.com/ubuntu noble-updates/main i386 Packages [261 kB]
Get:11 http://in.archive.ubuntu.com/ubuntu noble-updates/main Translation-en [117 kB]
Get:12 http://in.archive.ubuntu.com/ubuntu noble-updates/main amd64 c-n-f Metadata [7,716 B]
Get:13 http://in.archive.ubuntu.com/ubuntu noble-updates/universe i386 Packages [150 kB]
Get:14 http://in.archive.ubuntu.com/ubuntu noble-updates/universe amd64 Packages [337 kB]
Get:15 http://in.archive.ubuntu.com/ubuntu noble-updates/universe Translation-en [142 kB]
Get:16 http://in.archive.ubuntu.com/ubuntu noble-updates/universe amd64 c-n-f Metadata [13.7 kB]
Reading package lists... Done
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.ubuntu.com/ubuntu noble-security InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 871920D1991BC93C
E: The repository 'https://ppa.launchpadcontent.net/octave/stable/ubuntu noble Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
can someone help. thank you.
