EPOLLCTLDEL

EPOLL_CTL_DEL is a control operation used with the epoll_ctl system call on Linux to remove a file descriptor from an epoll instance. It is one of the three operations defined for epoll_ctl, alongside EPOLL_CTL_ADD and EPOLL_CTL_MOD. The operation targets a previously registered file descriptor and stops the kernel from monitoring events on that fd via the specified epoll instance.

The epoll_ctl function has the signature epoll_ctl(int epfd, int op, int fd, struct epoll_event *event). For EPOLL_CTL_DEL, the op parameter is EPOLL_CTL_DEL, the fd parameter is the file descriptor to remove, and the event parameter is typically ignored and may be NULL. The epoll instance referenced by epfd must have been created beforehand with epoll_create, epoll_create1, or a compatible API.

Behavior and return values: If the specified fd is currently registered with the epoll instance, it is removed and a successful return occurs. If the fd is not registered, EPOLL_CTL_DEL may fail with ENOENT. Other errors can include EINVAL for invalid arguments or EBADF for a bad epoll file descriptor. After a successful EPOLL_CTL_DEL, the file descriptor will no longer generate events on that epoll instance.

Common considerations: It is good practice to remove fds from epoll before closing them to avoid stray events. If you need to monitor an fd again, you must add it back with EPOLL_CTL_ADD. EPOLL_CTL_DEL does not affect other fds or the epoll instance itself.

See also: epoll, EPOLL_CTL_ADD, EPOLL_CTL_MOD, epoll_wait.