Engineering story
Make Linux sync progress visible
Read the engineering story for the design of live write-back monitoring and scoped follow mode.
Make Linux cache flushing observable
psync makes sync progress visible.
The standard sync command blocks until dirty pages are written without showing what remains. Psync polls Linux write-back counters while sync runs, reports elapsed time and a summary, and can watch a scoped target and resync when its files change.
go install codeberg.org/ubunatic/psync@latestOverview
Observe the flush while it runs
Psync starts sync(1) in the background and polls Dirty and Writeback in /proc/meminfo. It prints live progress and a completion summary without changing sync's behavior. Linux per-device write rates and in-flight requests are available when a target mount or device is selected.
psync -f /mnt/secure
psync -w /mnt/secure
psync -F important-file.dbCapabilities
Progress, watch, and scoped follow mode
Sync with progress
Poll system dirty/write-back counters while sync runs and print a summary.
Passive watch
Watch system write-back state without starting sync; target mode also reports device I/O.
Follow changed files
Resync a specific file or directory after changes, with debounce and minimum-interval guards.
Select a mount
Choose a mounted filesystem interactively when follow or watch mode needs a target.
Modes and options
Choose what psync observes
Default
Run sync and show live dirty/write-back progress and a completion summary.
-d / --data
Pass data-only mode to sync(1), without unneeded metadata.
-f / --file-system
Sync the filesystem that contains the selected target files.
-w / --watch
Observe write-back progress without calling sync(1).
-F / --follow
Watch selected files or direct directory entries and resync on changes.
--debounce and --min-interval
Coalesce change bursts and enforce a minimum delay between follow-mode syncs.
-i / --interval
Set how often psync samples /proc/meminfo; the default is 500 ms.
Safe follow mode
Follow only a target you choose
Follow mode requires a scoped file, directory, or selected filesystem. It does not infer targets from system-wide Dirty counters, so unrelated writes from other processes cannot trigger extra sync cycles. Directory watching is non-recursive.
Use psync demo to watch a deterministic simulated flush without writing test data to disk.
psync demo
psync demo --size-mb 8192 --duration 20sQuickstart
Install and try the simulation
Install from the latest Go module or download a release binary. Run psync demo to see the progress display without root access, a slow disk, or real disk writes.
go install codeberg.org/ubunatic/psync@latest
psync demoAt a glance
Stack
Go 1.26.5, Cobra, Loom, Linux /proc (meminfo, diskstats, mountinfo), inotify, GoReleaser
Milestones
Follow mode and mount picker in the first release (#006, f792678) · Per-device progress in watch mode (#011, 9279f9c) · Loom mount picker and v0.2.2 release (#013, 4485b28, 460d911)
Commits
26