Error while installing audit - linux

Question

While installing the sudo apt-get install auditd, i get this error:
Reading package lists... Done
Building dependency tree
Reading state information... Done
auditd is already the newest version (1:2.4.5-1ubuntu2.1).
The following package was automatically installed and is no longer required:
libprelude2v5
Use 'sudo apt autoremove' to remove it.
0 upgraded, 0 newly installed, 0 to remove and 706 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Setting up auditd (1:2.4.5-1ubuntu2.1) ...
update-rc.d: warning: start and stop actions are no longer supported; falling back to defaults
Job for auditd.service failed because the control process exited with error code. See "systemctl status auditd.service" and "journalctl -xe" for details.
invoke-rc.d: initscript auditd, action "restart" failed.
dpkg: error processing package auditd (--configure):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
auditd
E: Sub-process /usr/bin/dpkg returned an error code (1)
What is this error? How can i get rid of it?
And then i used this sudo apt-get install audit. Now i get this:
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package audit
Please help me. Thank you.
When i try sudo apt-get update , i get this :
Ign:1 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:2 http://dl.google.com/linux/chrome/deb stable Release
Get:3 http://packages.microsoft.com/repos/vscode stable InRelease [2,802 B]
Hit:5 http://archive.ubuntu.com/ubuntu xenial InRelease
Get:6 http://security.ubuntu.com/ubuntu xenial-security InRelease [107 kB]
Hit:7 http://in.archive.ubuntu.com/ubuntu xenial InRelease
Get:8 http://in.archive.ubuntu.com/ubuntu xenial-updates InRelease [109 kB]
Ign:9 http://apt.puppetlabs.com xenial InRelease
Get:10 http://apt.puppetlabs.com xenial Release [57.5 kB]
Get:11 http://apt.puppetlabs.com xenial Release.gpg [801 B]
Err:11 http://apt.puppetlabs.com xenial Release.gpg
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7F438280EF8D349F
Get:12 http://in.archive.ubuntu.com/ubuntu xenial-backports InRelease [107 kB]
Get:13 http://in.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages [785 kB]
Get:14 http://in.archive.ubuntu.com/ubuntu xenial-updates/main i386 Packages [720 kB]
Fetched 1,889 kB in 2s (678 kB/s)
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://apt.puppetlabs.com xenial Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7F438280EF8D349F
W: Failed to fetch http://apt.puppetlabs.com/dists/xenial/Release.gpg The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7F438280EF8D349F
W: Some index files failed to download. They have been ignored, or old ones used instead.