Not sure how to do it and what to look. I ran strace ./coolwsd and got a lot of output. It was a lot, so I paste something I think it may be helpful here:
socket(AF_INET6, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, IPPROTO_IP) = 14
setsockopt(14, SOL_TCP, TCP_NODELAY, [1], 4) = 0
getpid() = 139547
gettid() = 139547
setsockopt(14, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
setsockopt(14, SOL_IPV6, IPV6_V6ONLY, [0], 4) = 0
bind(14, {sa_family=AF_INET6, sin6_port=htons(9980), sin6_flowinfo=htonl(0), inet_pton(AF_INET6, "::", &sin6_addr), sin6_scope_id=0}, 28) = 0
getpid() = 139547
gettid() = 139547
listen(14, 64) = 0
getpid() = 139547
gettid() = 139547
getpid() = 139547
gettid() = 139547
write(2, "wsd-139547-139547 2025-03-26 14:"..., 536wsd-139547-139547 2025-03-26 14:26:58.728116 +0800 [ coolwsd ] DBG #14: Created socket. Thread affinity set to 0x7ec9f5a99880, Socket[#14, All @ :0]| net/Socket.hpp:474
wsd-139547-139547 2025-03-26 14:26:58.728645 +0800 [ coolwsd ] TRC #14: Bind to: IPv6 port: 9980| net/Socket.cpp:1149
wsd-139547-139547 2025-03-26 14:26:58.728869 +0800 [ coolwsd ] TRC #14: Listening| net/ServerSocket.hpp:81
wsd-139547-139547 2025-03-26 14:26:58.728999 +0800 [ coolwsd ] INF #14 Listening to client connections on port 9980| wsd/COOLWSD.cpp:3510
) = 536
getpid() = 139547
I’m sure in coolwsd.xml(.in) the proto is all and listen is any. It still looks like only bound to IPv6.
(There is a setsockopt setting the socket option as 'IPV6_V6only`. I’m not sure if it is the cause or not, or where it comes from.
The only place mentioning IPv4 in this strace log is
read(4, "IPv4-mapped IPv6 addresses\">::ff"..., 4092) = 4092
Here is the output of lsof when I ran strace ./coolwsd above:
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
coolwsd 139547 lodev cwd DIR 252,0 4096 1842768 /home/lodev/git/COOL
coolwsd 139547 lodev rtd DIR 252,0 4096 2 /
coolwsd 139547 lodev txt REG 252,0 79997992 1884790 /home/lodev/git/COOL/coolwsd
coolwsd 139547 lodev mem REG 252,0 5866528 2892100 /usr/lib/locale/locale-archive
coolwsd 139547 lodev mem REG 252,0 360460 2884339 /usr/lib/locale/C.utf8/LC_CTYPE
coolwsd 139547 lodev mem REG 252,0 2125328 2903539 /usr/lib/x86_64-linux-gnu/libc.so.6
coolwsd 139547 lodev mem REG 252,0 129256 2884837 /usr/lib/x86_64-linux-gnu/ossl-modules/legacy.so
coolwsd 139547 lodev mem REG 252,0 625344 2890413 /usr/lib/x86_64-linux-gnu/libpcre2-8.so.0.11.2
coolwsd 139547 lodev mem REG 252,0 952616 2903542 /usr/lib/x86_64-linux-gnu/libm.so.6
coolwsd 139547 lodev mem REG 252,0 2592224 2903090 /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.33
coolwsd 139547 lodev mem REG 252,0 26848 2899003 /usr/lib/x86_64-linux-gnu/libcap-ng.so.0.0.0
coolwsd 139547 lodev mem REG 252,0 170240 2884608 /usr/lib/x86_64-linux-gnu/libexpat.so.1.9.1
coolwsd 139547 lodev mem REG 252,0 133200 2886113 /usr/lib/x86_64-linux-gnu/libaudit.so.1.0.0
coolwsd 139547 lodev mem REG 252,0 183024 2897496 /usr/lib/x86_64-linux-gnu/libgcc_s.so.1
coolwsd 139547 lodev mem REG 252,0 293040 2896886 /usr/lib/x86_64-linux-gnu/libPocoCrypto.so.103
coolwsd 139547 lodev mem REG 252,0 2017952 2896883 /usr/lib/x86_64-linux-gnu/libPocoFoundation.so.103
coolwsd 139547 lodev mem REG 252,0 514240 2896897 /usr/lib/x86_64-linux-gnu/libPocoXML.so.103
coolwsd 139547 lodev mem REG 252,0 321720 2896889 /usr/lib/x86_64-linux-gnu/libPocoJSON.so.103
coolwsd 139547 lodev mem REG 252,0 448696 2896898 /usr/lib/x86_64-linux-gnu/libPocoUtil.so.103
coolwsd 139547 lodev mem REG 252,0 1366288 2896895 /usr/lib/x86_64-linux-gnu/libPocoNet.so.103
coolwsd 139547 lodev mem REG 252,0 67888 2899439 /usr/lib/x86_64-linux-gnu/libpam.so.0.85.1
coolwsd 139547 lodev mem REG 252,0 5305304 2884762 /usr/lib/x86_64-linux-gnu/libcrypto.so.3
coolwsd 139547 lodev mem REG 252,0 50 2884545 /usr/lib/locale/C.utf8/LC_NUMERIC
coolwsd 139547 lodev mem REG 252,0 113000 2899721 /usr/lib/x86_64-linux-gnu/libz.so.1.3
coolwsd 139547 lodev mem REG 252,0 3360 2884635 /usr/lib/locale/C.utf8/LC_TIME
coolwsd 139547 lodev mem REG 252,0 1406 2884322 /usr/lib/locale/C.utf8/LC_COLLATE
coolwsd 139547 lodev mem REG 252,0 270 2884541 /usr/lib/locale/C.utf8/LC_MONETARY
coolwsd 139547 lodev mem REG 252,0 48 2884504 /usr/lib/locale/C.utf8/LC_MESSAGES/SYS_LC_MESSAGES
coolwsd 139547 lodev mem REG 252,0 34 2884546 /usr/lib/locale/C.utf8/LC_PAPER
coolwsd 139547 lodev mem REG 252,0 62 2884544 /usr/lib/locale/C.utf8/LC_NAME
coolwsd 139547 lodev mem REG 252,0 127 2884281 /usr/lib/locale/C.utf8/LC_ADDRESS
coolwsd 139547 lodev mem REG 252,0 47 2884576 /usr/lib/locale/C.utf8/LC_TELEPHONE
coolwsd 139547 lodev mem REG 252,0 23 2884398 /usr/lib/locale/C.utf8/LC_MEASUREMENT
coolwsd 139547 lodev mem REG 252,0 27028 2903528 /usr/lib/x86_64-linux-gnu/gconv/gconv-modules.cache
coolwsd 139547 lodev mem REG 252,0 258 2884341 /usr/lib/locale/C.utf8/LC_IDENTIFICATION
coolwsd 139547 lodev mem REG 252,0 236616 2903536 /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2
coolwsd 139547 lodev 0u CHR 136,1 0t0 4 /dev/pts/1
coolwsd 139547 lodev 1w REG 252,0 1568428 1861625 /home/lodev/git/COOL/strace.log
coolwsd 139547 lodev 2w REG 252,0 1568428 1861625 /home/lodev/git/COOL/strace.log
coolwsd 139547 lodev 3r CHR 1,9 0t0 10 /dev/urandom
coolwsd 139547 lodev 4r FIFO 0,15 0t0 146612 pipe
coolwsd 139547 lodev 5w FIFO 0,15 0t0 146612 pipe
coolwsd 139547 lodev 6r FIFO 0,15 0t0 146613 pipe
coolwsd 139547 lodev 7w FIFO 0,15 0t0 146613 pipe
coolwsd 139547 lodev 8r FIFO 0,15 0t0 146614 pipe
coolwsd 139547 lodev 9w FIFO 0,15 0t0 146614 pipe
coolwsd 139547 lodev 10r FIFO 0,15 0t0 146615 pipe
coolwsd 139547 lodev 11w FIFO 0,15 0t0 146615 pipe
coolwsd 139547 lodev 12r FIFO 0,15 0t0 146618 pipe
coolwsd 139547 lodev 13w FIFO 0,15 0t0 146618 pipe
coolwsd 139547 lodev 14u IPv6 146619 0t0 TCP *:9980 (LISTEN)
coolwsd 139547 lodev 15u unix 0x0000000000000000 0t0 146620 @coolwsd-aJqZVnv6@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ type=STREAM (LISTEN)
Looks like it only listen to IPv6 as well.