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| NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON | |
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sync(2) System Calls Manual sync(2) sync, syncfs - commit filesystem caches to disk
Standard C library (libc, -lc)
#include <unistd.h> void sync(void); int syncfs(int fd); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): sync(): _XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE syncfs(): _GNU_SOURCE
sync() causes all pending modifications to filesystem metadata and cached file data to be written to the underlying filesystems. syncfs() is like sync(), but synchronizes just the filesystem containing file referred to by the open file descriptor fd.
syncfs() returns 0 on success; on error, it returns -1 and sets errno to indicate the error.
sync() is always successful. syncfs() can fail for at least the following reasons: EBADF fd is not a valid file descriptor. EIO An error occurred during synchronization. This error may relate to data written to any file on the filesystem, or on metadata related to the filesystem itself. ENOSPC Disk space was exhausted while synchronizing. ENOSPC EDQUOT Data was written to a file on NFS or another filesystem which does not allocate space at the time of a write(2) system call, and some previous write failed due to insufficient storage space.
According to the standard specification (e.g., POSIX.1-2001), sync() schedules the writes, but may return before the actual writing is done. However Linux waits for I/O completions, and thus sync() or syncfs() provide the same guarantees as fsync() called on every file in the system or filesystem respectively.
sync() POSIX.1-2008. syncfs() Linux.
sync() POSIX.1-2001, SVr4, 4.3BSD. syncfs() Linux 2.6.39, glibc 2.14. Since glibc 2.2.2, the Linux prototype for sync() is as listed above, following the various standards. In glibc 2.2.1 and earlier, it was "int sync(void)", and sync() always returned 0. In mainline kernel versions prior to Linux 5.8, syncfs() will fail only when passed a bad file descriptor (EBADF). Since Linux 5.8, syncfs() will also report an error if one or more inodes failed to be written back since the last syncfs() call.
Before Linux 1.3.20, Linux did not wait for I/O to complete before returning.
sync(1), fdatasync(2), fsync(2)
This page is part of the man-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which is not part of the original manual page), send a mail to man-pages@man7.org Linux man-pages 6.15 2025-05-17 sync(2) Pages that refer to this page: sync(1), systemd-nspawn(1), bdflush(2), fsync(2), mount(2), reboot(2), sync_file_range(2), syscalls(2), fclose(3), fflush(3), nfs(5), ctrlaltdel(8), fdisk(8), fsck.minix(8), mke2fs(8), mount(8), xfs_io(8), xfs_quota(8)
| HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. | |