lvmpolld

Start the daemon in the foreground

$ lvmpolld [[-f|--foreground]]

$ lvmpolld [[-f|--foreground]] [[-l|--log]] debug

$ lvmpolld [[-t|--timeout]] [300]

$ lvmpolld [[-s|--socket]] [/tmp/lvmpolld.socket]

$ lvmpolld [[-p|--pidfile]] [/tmp/lvmpolld.pid]

$ lvmpolld --dump

lvmpolld [OPTIONS]

-h, --help
    Displays a help message and exits.

-V, --version
    Prints the version number and exits.

-f, --foreground
    Runs the daemon in the foreground, primarily for debugging purposes.

-l, --readonly
    Runs the daemon in read-only mode, preventing any modifications.

-s, --socket=Path
    Specifies the path for the daemon's communication socket.

-p, --pidfile=Path
    Specifies the path for the daemon's PID file.

-o, --driveropts=String
    Passes additional driver-specific options to the LVM backend.

-d, --debug
    Increases the debugging level for more verbose output.

-v, --verbose
    Increases the verbosity of the output.

-q, --quiet
    Suppresses informational and warning messages.

The lvmpolld daemon is a crucial component of the Logical Volume Manager (LVM) in Linux, responsible for monitoring and managing long-running LVM operations that occur in the background.

Historically, some LVM operations like pvmove (moving extents between physical volumes), lvconvert --mirror (creating or converting logical volumes to mirrors), or lvchange --resync (resynchronizing mirrored or RAID logical volumes) would either block the calling command until completion or rely on kernel mechanisms. lvmpolld centralizes this polling, allowing these operations to proceed asynchronously.

It periodically checks the progress and status of these background tasks, updating LVM metadata and ensuring proper completion. This daemon typically starts automatically with the LVM system services (e.g., lvm.systemd.service) when such operations are initiated. Its primary function is to prevent LVM commands from blocking for extended periods and to ensure the integrity and completion of complex, time-consuming LVM processes.

If lvmpolld is not running, background LVM operations will not be monitored and may not complete, potentially leading to stalled or inconsistent LVM states.

If lvmpolld is stopped or not running, LVM operations that require background polling (e.g., pvmove, lvconvert --mirror, lvchange --resync) will halt their progress and may remain in an incomplete or inconsistent state. Ensuring its continuous operation is critical for the reliability of such LVM features.

While it runs in the background, excessive logging or a very high polling frequency (if configurable, though not directly exposed via standard options) could theoretically consume system resources, but this is rarely an issue in practice due to its optimized design.

lvmpolld operates as a system daemon, usually starting automatically via systemd (e.g., lvm.systemd.service) when LVM detects an active background operation. It communicates with LVM tools via a local socket, receiving requests for polling and reporting status updates. Its continuous operation is vital for the integrity and completion of LVM tasks like pvmove or mirror synchronizations. Manual intervention to start or stop it is typically only required for debugging or advanced troubleshooting.

The introduction of lvmpolld marked a significant improvement in how LVM handles background operations. Prior to its existence, such tasks were often either blocking or managed in a less centralized manner. The daemon was introduced to provide a robust, consistent, and non-blocking mechanism for monitoring the progress of these operations, enhancing the overall reliability and user experience of LVM when dealing with complex data movements and synchronizations. It became an integral part of modern LVM installations, typically managed by system init systems like systemd.

lvm(8), pvmove(8), lvconvert(8), lvchange(8), vgchange(8)