In UNIX and UNIX-like operating systems like Linux, the **`sync`** command is used to synchronize file data in the main memory with the persistent storage. 

Since writing to a file is done in an asynchronous manner, the writes are cached in the memory until it is the appropriate time to write them to the disk. This frees up the CPU to do other tasks while files are written to the disk.

The `sync` command forces the file writes in the main memory cache and the disk to synchronize.

# Syntax
```Shell
sync [[-d | --data] | [-f | --file-system]] [file …]
```

# Parameters
* **`-d or --data`**: This is used to only sync file data and the minimum metadata needed to maintain filesystem consistency.

* **`-f or --file-system`**: This is used when you want to sync up all the pending I/O and all the referenced files inside the filesystem.

* **`file...`**: The names of one or more files specified. If no file is specified, all the mounted files are synchronized. 

It is uncommon to manually use the `sync` command. Generally speaking, the `sync` command is only used prior to performing tasks that may make the kernel unstable or are known to cause crashes.

# Examples

To sync up all cached files of the current user:
```Shell
sync
```

To sync all mounted systems:
```Shell
sudo sync
```

To sync just two files:
```Shell
sync $HOME/file1 $HOME/file2
```

To sync up only the data and minimal metadata of two files:
```Shell
sync -d $HOME/file1 $HOME/file2
```



What is Linux trigger syncing?

Sync synchronizes file data in memory with persistent storage, using -d for minimal metadata or -f for full filesystem.