|FSYNC(2)||Linux Programmer's Manual||FSYNC(2)|
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Glibc 2.16 and later:
No feature test macros need be defined
Glibc up to and including 2.15:
_BSD_SOURCE || _XOPEN_SOURCE
|| /* since glibc 2.8: */ _POSIX_C_SOURCE >= 200112L
_POSIX_C_SOURCE >= 199309L || _XOPEN_SOURCE >= 500 inode(7)). Calling fsync() does not necessarily ensure that the entry in the directory containing the file has also reached disk. For that an explicit fsync() on a file descriptor for the directory is also needed. fdatasync() is similar to fsync(), but does not flush modified metadata unless that metadata is needed in order to allow a subsequent data retrieval to be correctly handled. For example, changes to st_atime or st_mtime (respectively, time of last access and time of last modification; see inode(7)) do not require flushing because they are not necessary for a subsequent data read to be handled correctly. On the other hand, a change to the file size (st_size, as made by say ftruncate(2)), would require a metadata flush. The aim of fdatasync() is to reduce disk activity for applications that do not require all metadata to be synchronized with the disk.
- fd is not a valid open file descriptor.
- An error occurred during synchronization. This error may relate to data written to some other file descriptor on the same file. Since Linux 4.13, errors from write-back will be reported to all file descriptors that might have written the data which triggered the error. Some filesystems (e.g., NFS) keep close track of which data came through which file descriptor, and give more precise reporting. Other filesystems (e.g., most local filesystems) will report errors to all file descriptors that where open on the file when the error was recorded.
- Disk space was exhausted while synchronizing.
- EROFS, EINVAL
- fd is bound to a special file (e.g., a pipe, FIFO, or socket) which does not support synchronization.
- ENOSPC, EDQUOT
- fd is bound 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.