Only pipe STDERR output in `bash` with timestamp

Posted on 20/12/202221/12/2022 by Bian Xi Leave a Comment

Only pipe STDERR output in `bash` with timestamp

`bash`

In order to discard standard output and only log the standard error, following command can be used. The second part of command is to prefix the current timestamp in the output

sh monitor 2>&1>/dev/null | ts '[%Y-%m-%d %H:%M:%S]'

`dash`

If need to run in dash, such as running in crontab, above syntax is wrong, use following command instead

sh monitor 3>&1 1>/dev/null 2>&3 3>&- | ts '[%Y-%m-%d %H:%M:%S]'

Note: This command can be run in bash too

References

Prepending a timestamp to each line of output from a command
Pipe only STDERR through a filter

Apply filter to STDERR in Linux

Posted on 20/12/202221/12/2022 by Bian Xi Leave a Comment

Apply filter to STDERR in Linux

STDOUT ────────────────┐
                       ├─────> terminal/file/whatever
STDERR ── [ filter ] ──┘

Method

If ./a.out outputs as below

In STDERR:

stderr output

In STDOUT:

more regular

Then the following command will output as below.

# ./a.out 3>&1 1>&2 2>&3 3>&- | sed 's/e/E/g'
more regular
stdErr output

Explanation

    First save stdout as &3 (&1 is duped into 3)
    Next send stdout to stderr (&2 is duped into 1)
    Send stderr to &3 (stdout) (&3 is duped into 2)
    close &3 (&- is duped into 3)

References

Pipe only STDERR through a filter

Fix Spice Certificate Issue in Proxmox

Posted on 20/12/2022 by Bian Xi Leave a Comment

Fix Spice Certificate Issue in Proxmox

After changed the display to Spice and added Spice USB device, following error appeared.

swtpm_setup: Not overwriting existing state file.
kvm: warning: Spice: reds.c:2893:reds_init_ssl: Could not load certificates from /etc/pve/local/pve-ssl.pem
kvm: warning: Spice: error:0909006C:PEM routines:get_name:no start line
kvm: warning: Spice: error:140DC009:SSL routines:use_certificate_chain_file:PEM lib
kvm: failed to initialize spice server
stopping swtpm instance (pid 55260) due to QEMU startup error
TASK ERROR: start failed: QEMU exited with code 1

Update certificate also got following errors

root@pve01:~# pvecm updatecerts --force
(re)generate node files
generate new node certificate
Signature ok
subject=OU = PVE Cluster Node, O = Proxmox Virtual Environment, CN = pve01.xxx.net
Getting CA Private Key
CA certificate and CA private key do not match
139954545105792:error:06067099:digital envelope routines:EVP_PKEY_copy_parameters:different parameters:../crypto/evp/p_lib.c:93:
139954545105792:error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch:../crypto/x509/x509_cmp.c:303:
unable to generate pve ssl certificate:
command 'faketime yesterday openssl x509 -req -in /tmp/pvecertreq-56235.tmp -days 161 -out /etc/pve/nodes/pve01/pve-ssl.pem -CAkey /etc/pve/priv/pve-root-ca.key -CA /etc/pve/pve-root-ca.pem -CAserial /etc/pve/priv/pve-root-ca.srl -extfile /tmp/pvesslconf-56235.tmp' failed: exit code 1

In this case, remove keys and regenerate.

root@pve01:~# rm -f /etc/pve/pve-root-ca.pem /etc/pve/priv/pve-root-ca.* /etc/pve/local/pve-ssl.*
root@pve01:~# pvecm updatecerts -f
(re)generate node files
generate new node certificate
merge authorized SSH keys and known hosts
root@pve01:~# pvecm updatecerts -f
(re)generate node files
generate new node certificate
merge authorized SSH keys and known hosts
root@pve01:~#

Now, problem fixed.

References

pveproxy fails to load local certificate chain after upgrade to pve 6

Error encountered during `apt install` indicated that the file couldn’t be accessed by user `_apt`

Posted on 20/12/2022 by Bian Xi Leave a Comment

Error encountered during `apt install` indicated that the file couldn't be accessed by user `_apt`

When installing package from local file (.deb file), following error might be occurred.

Processing triggers for dbus (1.14.0-2ubuntu3) ...
N: Download is performed unsandboxed as root as file 'full_path_of_deb_file_name' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)

Usually apt tries to run the process that fetches packages as a different user called _apt to increase security. That's no problem if it has to download packages from the internet. But if you tell it to install a .deb file that's already on your system, it needs to have permission to access that file by _apt user. Otherwise, above error will be shown.