It’s important to distinguish between the file descriptor, which is a small integer that the process uses in its read and write calls to identify the file, and the file description, which is a structure in the kernel. The file offset is part of the file description. It lives in the kernel. As an example, … Read more
ulimit -n 10000 That might not work depending on you system configuration Consult this to configure your system.
The select() system call tells you whether there is any data to read on the file descriptors that you’re interested in. Strictly, it is a question of whether a read operation on the file descriptor will block or not. If you execute read() on a file descriptor — such as that connected to a serial … Read more
I had a hard time getting Activity Monitor to show open files for a process that was running as root (via sudo). The original question mentions lsof, and it does the trick exactly. If you know the process name or PID, it’s super quick. Find processes by name: lsof -c processname Find processes by PID: … Read more
File descriptors 0, 1 and 2 are for stdin, stdout and stderr respectively. File descriptors 3, 4, .. 9 are for additional files. In order to use them, you need to open them first. For example: exec 3<> /tmp/foo #open fd 3. echo “test” >&3 exec 3>&- #close fd 3. For more information take a … Read more
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
Just use: position = lseek(fd, 0, SEEK_CUR);
You need to add the O_WRONLY flag : if f, err := os.OpenFile(“./log.log”, os.O_APPEND|os.O_WRONLY, os.ModeAppend); err != nil { /*[…]*/ } To explain, here is the linux documentation for open: http://man7.org/linux/man-pages/man2/openat.2.html : The argument flags must include one of the following access modes: O_RDONLY, O_WRONLY, or O_RDWR. These request opening the file read- only, write-only, … Read more
While portable, closing all file descriptors up to sysconf(_SC_OPEN_MAX) is not reliable, because on most systems this call returns the current file descriptor soft limit, which could have been lowered below the highest used file descriptor. Another issue is that on many systems sysconf(_SC_OPEN_MAX) may return INT_MAX, which can cause this approach to be unacceptably … Read more
fcntl(fd, F_GETFD) is the canonical cheapest way to check that fd is a valid open file descriptor. If you need to batch-check a lot, using poll with a zero timeout and the events member set to 0 and checking for POLLNVAL in revents after it returns is more efficient. With that said, the operation “check … Read more