syncfs

Syncfs is a Linux system call that synchronizes all in-memory data and metadata for the filesystem that contains the file referred to by the provided file descriptor. It ensures that pending writes and metadata changes are flushed to the underlying storage. The call is identified as int syncfs(int fd) and is available on Linux in userspace programs via the C library as a wrapper around the kernel system call.

This call differs from fsync, which operates on a single open file object and ensures its inodes and data are written to disk; syncfs, by contrast, targets the entire filesystem that the fd belongs to, flushing all dirty inodes and metadata associated with that filesystem. It is also distinct from the generic sync() call, which flushes buffered data to disk for all filesystems and can be less predictable in timing.

Usage: A process calls syncfs with a file descriptor referencing any file on the target filesystem. On success, 0 is returned; on error, -1 is returned and errno is set. Common error codes include EBADF for an invalid fd, and EROFS if the filesystem is read-only or otherwise cannot be synchronized.

Notes: syncfs is Linux-specific and not specified by POSIX; the exact behavior can vary across filesystem implementations. It can be useful after a crash, before unmounting, or when ensuring that metadata and data are persisted for a whole filesystem.