listen(2) System Calls Manual listen(2) listen - (libc -lc) #include int listen(int sockfd, int backlog); listen() sockfd accept(2). sockfd SOCK_STREAM SOCK_SEQPACKET. backlog sockfd. ECONNREFUSED . . -1 errno . EADDRINUSE . EADDRINUSE ( ) sockfd (ephemeral) . /proc/sys/net/ipv4/ip_local_port_range ip(7). EBADF sockfd . ENOTSOCK sockfd . EOPNOTSUPP listen(). POSIX.1-2024. 4.2BSD, POSIX.1-2001. : (1) socket(2). (2) bind(2) connect(2). (3) listen(). (4) accept(2). backlog TCP Linux 2.2. . /proc/sys/net/ipv4/tcp_max_syn_backlog. . tcp(7) . backlog /proc/sys/net/core/somaxconn . Linux 5.4 4096 128. Linux 2.4.25 SOMAXCONN 128. bind(2). accept(2), bind(2), connect(2), socket(2), socket(7) 3 . . : . 6.18 11 2026 listen(2)