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What happens if FD is the last file descriptor?
If fd is the last file descriptor referring to the underlying open file description (see open (2)), the resources associated with the open file description are freed; if the file descriptor was the last reference to a file which has been removed using unlink (2), the file is deleted. close () returns zero on success.
What happens when you close a file descriptor in Linux?
This can occur because the Linux kernel always releases the file descriptor early in the close operation, freeing it for reuse; the steps that may return an error, such as flushing data to the filesystem or device, occur only later in the close operation.
How to find and remove deleted files in process?
If you don’t know the pid, and are looking for deleted files, you can do: lsof -nP | grep ‘ (deleted)’. lsof -nP +L1, as mentioned by @user75021 is an even better (more reliable and more portable) option (list files that have fewer than 1 link). Or (on Linux): find /proc/*/fd -ls | grep ‘ (deleted)’.
How to test a file descriptor in Linux?
For Linux atleast, [ [ -e /dev/fd/$ {FD} ]] will do, where FD is the bash-variable that stores the FD you want to test. The command succeeds when FD is open, fails otherwise. The question is quite old – but anyway – why just do not use builtins?
Is it safe to close a file descriptor?
It is probably unwise to close file descriptors while they may be in use by system calls in other threads in the same process. Since a file descriptor may be reused, there are some obscure race conditions that may cause unintended side effects.
Which is an example of a file descriptor?
File descriptors can also refer to other objects that do not normally exist in the file system, such as anonymous pipes and network sockets. The FILE data structure in the C standard I/O library usually includes a low level file descriptor for the object in question on Unix-like systems.
Where do I find the file descriptor in Linux?
On Linux, the set of file descriptors open in a process can be accessed under the path /proc/PID/fd/, where PID is the process identifier. In Unix-like systems, file descriptors can refer to any Unix file type named in a file system.