11-19-2013
Quote:
Originally Posted by
acascianelli
I have a Linux server that runs a Java based app that automates file transfers for a large number of users/systems. I'm running into a problem with the scripts for this automation program in that when I have a function in the script generate an output file, and the next line requires that file to be present; the script will fail because the file hasn't made it to disk yet.
sync is irrelevant -- a file in cache is as good as a file on disk as far as programs are concerned. The file must really be
missing, even from cache, a sync won't force it to appear. It's the wait that does the trick either way.
Both
sync and short delays are liable to fail I think -- particularly when the system is busy and longer delays might happen. Either correct the java program so it doesn't return until the file actually exists, or poll for the file's existence every so often.
Quote:
My question is, could there be any undesired side affects to running the 'sync' command so often on a system?
Reduced disk performance since its busy doing more writes all the time. It may end up writing more than it would have otherwise, too.
Last edited by Corona688; 11-19-2013 at 12:24 PM..
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LEARN ABOUT CENTOS
syncfs
SYNC(2) Linux Programmer's Manual SYNC(2)
NAME
sync, syncfs - commit buffer cache to disk
SYNOPSIS
#include <unistd.h>
void sync(void);
int syncfs(int fd);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sync():
_BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
syncfs():
_GNU_SOURCE
DESCRIPTION
sync() causes all buffered modifications to file metadata and data to be written to the underlying file systems.
syncfs() is like sync(), but synchronizes just the file system containing file referred to by the open file descriptor fd.
RETURN VALUE
syncfs() returns 0 on success; on error, it returns -1 and sets errno to indicate the error.
ERRORS
sync() is always successful.
syncfs() can fail for at least the following reason:
EBADF fd is not a valid file descriptor.
VERSIONS
syncfs() first appeared in Linux 2.6.39; library support was added to glibc in version 2.14.
CONFORMING TO
sync(): SVr4, 4.3BSD, POSIX.1-2001.
syncfs() is Linux-specific.
NOTES
Since glibc 2.2.2 the Linux prototype for sync() is as listed above, following the various standards. In libc4, libc5, and glibc up to
2.2.1 it was "int sync(void)", and sync() always returned 0.
BUGS
According to the standard specification (e.g., POSIX.1-2001), sync() schedules the writes, but may return before the actual writing is
done. However, since version 1.3.20 Linux does actually wait. (This still does not guarantee data integrity: modern disks have large
caches.)
SEE ALSO
bdflush(2), fdatasync(2), fsync(2), sync(8), update(8)
COLOPHON
This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2012-05-04 SYNC(2)