Translation: libvirt: debug and logging

译libvirt : debug and logging

You need to use some functions of libvirt to start the virtual machine, but qemu needs to print the log. libvirt gives the corresponding solution:

• LIBVIRT_DEBUG
• LIBVIRT_LOG_FILTERS
• LIBVIRT_LOG_OUTPUTS

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Markdown and extensions

The logging facility in libvirt is based on 3 key concepts.

variable	value
Log messages	DEBUG = 1, INFO = 2, WARNING = 3, ERROR = 4
Log filters	x:name
Log outputs	filename

log messages represent the log level, and only output information whose log level is higher than the set level

    1 (or debug) - log all messages
    2 (or info) - log all non-debugging information
    3 (or warn) - log only warnings and errors - this is the default
    4 (or error) - log only errors 

log filters indicate that the log output content is related

1:qemu //输出qemu相关的调试信息，日志等级为debug

log outputs represents the output path

x:stderr - log to stderr
x:syslog:name - log to syslog with a prefix of "name"
x:file:file_path - log to a file specified by "file_path"

Example
LIBVIRT_DEBUG=error LIBVIRT_LOG_FILTERS=”1:qemu” LIBVIRT_LOG_OUTPUTS=”/var/log/libvirt/qemu/ubuntu12.log” virsh start ubuntu12
analysis:
start the Ubuntu2 virtual machine, enable log output: output information above the virsh error level, and Output the information above the qemu debug level to the /var/log/libvirt/qemu/ubuntu12.log file