# sync

_Peios / Using Peios / Peiosutils / System and processes_

> Flush cached writes out to persistent storage.

`sync` flushes cached writes to persistent storage.

```
sync [options] [file...]
```

```
$ sync
```

When a program writes to a file, the data does not always reach the physical device immediately — for speed, the system holds recent writes in memory and writes them out a little later. `sync` forces that pending data out *now*, so that what is on the device matches what programs have written.

It is the command to run before doing something that should not lose recent writes — before powering off by hand, or before removing storage.

## Options

With no argument, `sync` flushes everything. The options narrow it:

| Option | Effect |
|---|---|
| `file...` | Flush only the given files, rather than everything. |
| `-d`, `--data` | For the given files, flush only the file data, not metadata that does not need it. |
| `-f`, `--file-system` | Flush the entire file system that contains each given file. |

## Exit status

| Code | Meaning |
|---|---|
| `0` | The flush completed. |
| `1` | A named file could not be reached. |

Related content:

- [System and processes](/peios/using-peios/peiosutils/system-and-processes/overview.md)