Check the open FD limit for a given process in Linux
Count the entries in /proc/<pid>/fd/. The hard and soft limits applying to the process can be found in /proc/<pid>/limits.
file-descriptor
What can lead to “IOError: [Errno 9] Bad file descriptor” during os.system()?
You get this error message if a Python file was closed from “the outside”, i.e. not from the file object’s close() method: >>> f = open(“.bashrc”) >>> os.close(f.fileno()) >>> del f close failed in file object destructor: IOError: [Errno 9] Bad file descriptor The line del f deletes the last reference to the file object, … Read more
How to construct a c++ fstream from a POSIX file descriptor?
From the answer given by Éric Malenfant: AFAIK, there is no way to do this in standard C++. Depending on your platform, your implementation of the standard library may offer (as a nonstandard extension) a fstream constructor taking a file descriptor as input. (This is the case for libstdc++, IIRC) or a FILE*. Based on … Read more
What does >& mean?
This is the same as &>. From the bash manpage: Redirecting Standard Output and Standard Error This construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be redirected to the file whose name is the expansion of word. There are two formats for redirecting standard output … Read more
Retrieve filename from file descriptor in C
You can use readlink on /proc/self/fd/NNN where NNN is the file descriptor. This will give you the name of the file as it was when it was opened — however, if the file was moved or deleted since then, it may no longer be accurate (although Linux can track renames in some cases). To verify, … Read more
What’s the difference between a file descriptor and file pointer?
A file descriptor is a low-level integer “handle” used to identify an opened file (or socket, or whatever) at the kernel level, in Linux and other Unix-like systems. You pass “naked” file descriptors to actual Unix calls, such as read(), write() and so on. A FILE pointer is a C standard library-level construct, used to … Read more
What is the theoretical maximum number of open TCP connections that a modern Linux box can have
A single listening port can accept more than one connection simultaneously. There is a ’64K’ limit that is often cited, but that is per client per server port, and needs clarifying. Each TCP/IP packet has basically four fields for addressing. These are: source_ip source_port destination_ip destination_port <—– client ——> <——— server ————> Inside the TCP … Read more
What are file descriptors, explained in simple terms?
In simple words, when you open a file, the operating system creates an entry to represent that file and store the information about that opened file. So if there are 100 files opened in your OS then there will be 100 entries in OS (somewhere in kernel). These entries are represented by integers like (…100, … Read more