Turning on debug logs
If you report a bug against libvirt, in most cases you will be asked to attach debug logs. These are bare text files which tracks transition between different states of libvirtd, what it has tried to achieve, etc. Because of client -- server schema used in libvirt, the logs can be either client or server too. Usually, it's server side that matters as nearly all interesting work takes place there. Moreover, libvirt catches stderr of all running domains. These can be useful as well.
How to turn on debug logs for libvirt
The daemon configuration files location is dependent on connection URI. For
/etc/libvirt/libvirtd.confin your favourite editor
- find & replace, or set these variables:
# LEGACY SETTINGS PRIOR LIBVIRT 4.4.0 SEE BELOW! # log_level = 1 log_filters="3:remote 4:event 3:json 3:rpc" log_outputs="1:file:/var/log/libvirt/libvirtd.log"
# PREFERRED SETTINGS AFTER LIBVIRT 4.4.0 # log_filters="3:remote 4:event 3:json 3:rpc 1:*" log_outputs="1:file:/var/log/libvirt/libvirtd.log"
- save and exit
- restart libvirtd service
systemctl restart libvirtd.service
In the config variables above, we have set logging level to 1 (debug level), set some filters (to filter out noise), e.g. from rpc only warnings (=level 3) and above will be reported. The logs are saved into
/var/log/libvirt/libvirtd.log. Since libvirt 4.4.0 log filters support shell globbing, therefore the usage of
log_level is considered deprecated in favour of pure usage of
In case you want to get the client logs, you need to set this environment variable:
However, when you are using the session mode
qemu:///session or you run the
libvirtd as unprivileged user you will find configuration file under
Debugging anomalies can be very painful, especially when trying to reproduce it after the daemon restarts, since the new session can make the anomaly "disappear". Therefore, it's possible to enable the debug logs during runtime using libvirt administration API. To use it conveniently, there's a virt-admin client provided by the libvirt-admin package. Use the package manager provided by your distribution to install this package. Once you have it installed, run the following as root to see the set of log filters currently being active:
# virt-admin daemon-log-filters Logging filters: 3:remote 4:json 4:rpc
In order to change this set, run the same command as root, this time with your own set of filters:
## LEGACY APPROACH ENUMERATING ALL THE DESIRED MODULES ## # virt-admin daemon-log-filters "1:util 1:libvirt 1:storage 1:network 1:nodedev 1:qemu"
## CURRENT APPROACH USING SHELL GLOBBING ## # virt-admin daemon-log-filters "3:remote 4:json 4:rpc 1:*"
Analogically, the same procedure can be performed with log outputs:
# virt-admin daemon-log-outputs Logging outputs: 3:syslog:libvirtd # virt-admin daemon-log-outputs "1:file:/var/log/libvirt/libvirtd.log"
NOTE: It's always good practice to return the settings to the original state once you're finished debugging, just remember to save the original sets of filters and outputs and restore them at the end the same way as described above.
Removing filters and outputs
It's also possible to remove all the filters and produce an enormous log file, but it is not recommended since some of libvirt's modules can produce a large amount of noise. However, should you really want to do this, you can specify an empty set of filters:
# virt-admin daemon-log-filters "" Logging filters:
The situation is a bit different with outputs, since libvirt always has to log somewhere and resetting the outputs to an empty set will restore the default setting which depends on the host configuration, journald in our case:
# virt-admin daemon-log-outputs Logging outputs: 1:file:/var/log/libvirt/libvirtd.log # virt-admin daemon-log-outputs "" Logging outputs: 2:journald
What to attach?
Now you should go and reproduce the bug. Once you're finished, attach:
/var/log/libvirt/libvirtd.logor whatever path you set for the daemon logs.
- If the problem is related to a domain attach
/var/log/libvirt/qemu/$dom.logthen. Or substitute
qemuwith whatever hypervisor you are using.
- If you are asked for client logs,