Why deleted files still use space.
WHAT A FILE DESCRIPTOR IS
A process's handle to an open file.
WHY IT MATTERS PRACTICALLY
Space is only released when the last handle closes, not when the name is deleted.
WHAT THAT PRODUCES
A disk reporting full while the files appear gone.
HOW TO SEE IT
lsof filtered for deleted entries.
WHAT TO DO
Restart the process holding it, or truncate the file through its handle.
WHY RESTARTING WORKS
It closes the handle, releasing the space.
WHAT COMMONLY CAUSES THIS
Deleting a log file without telling the service to reopen it.
WHAT TO DO INSTEAD OF DELETING A LIVE LOG
Truncate it, which keeps the handle valid.
WHAT AN OPEN FILE LIMIT IS
A cap on how many files a process may hold at once.
WHAT EXCEEDING IT PRODUCES
Errors about too many open files.
WHERE THAT ARISES
Busy web servers and databases.
HOW TO SEE THE LIMIT
The limits for a running process, or the configured value.
WHAT TO RAISE
Both the system-wide maximum and the service's own limit.
WHY BOTH
Raising one without the other has no effect.
WHAT TO CHECK AFTER RAISING IT
That it actually applied to the running service.
