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I have some issue with dnsmasq. I'm trying to use the existing dhcp that is provide by my router to create a pxe server but dnsmasq give me an errror.

/etc/dnsmasq.conf :

port=0 log-dhcp dhcp-range=192.168.0.0,proxy dhcp-boot=pxelinux.0 pxe-service=x86PC,'Network Boot',pxelinux enable-tftp tftp-root=/tftpboot

the error :

● dnsmasq.service - DNS caching server. Loaded: loaded (/usr/lib/systemd/system/dnsmasq.service; disabled; vendor preset: disabled) Active: failed (Result: exit-code) since Sat 2022-05-07 14:50:57 CEST; 1s ago Process: 22959 ExecStart=/usr/sbin/dnsmasq -k (code=exited, status=2) Main PID: 22959 (code=exited, status=2) mai 07 14:50:57 host.dynamic.voo.be systemd[1]: Started DNS caching server.. mai 07 14:50:57 host.dynamic.voo.be dnsmasq[22959]: dnsmasq: failed to bind DHCP server socket: Address already in use mai 07 14:50:57 host.dynamic.voo.be dnsmasq[22959]: failed to bind DHCP server socket: Address already in use mai 07 14:50:57 host.dynamic.voo.be systemd[1]: dnsmasq.service: Main process exited, code=exited, status=2/INVALIDARGUMENT mai 07 14:50:57 host.dynamic.voo.be dnsmasq[22959]: FAILED to start up mai 07 14:50:57 host.dynamic.voo.be systemd[1]: dnsmasq.service: Failed with result 'exit-code'.

The interface configuration :

2: eno1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000 link/ether 10:e7:c6:16:55:8b brd ff:ff:ff:ff:ff:ff inet 192.168.0.100/24 brd 192.168.0.255 scope global noprefixroute eno1 valid_lft forever preferred_lft forever inet6 2a02:2788:7d4:66b::9/128 scope global dynamic noprefixroute valid_lft 912066sec preferred_lft 307266sec inet6 2a02:2788:7d4:66b:aca7:f9f4:3c57:9d62/64 scope global dynamic noprefixroute valid_lft 1209592sec preferred_lft 604792sec inet6 fe80::7f8c:47f6:d123:7c38/64 scope link noprefixroute valid_lft forever preferred_lft forever

My dhcp parameter on my router :

ip of my router : 192.168.0.1 1st address : 192.168.0.10 last address : 192.168.0.99 release time in sec : 604800

regards,

stickman

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    So is there an other DHCP server already running on the system? Commented May 7, 2022 at 15:43

2 Answers 2

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In essence I do not see any real problems with your setup or config. I've tested if dnsmasq is able to start up OK with the provided .conf file and it can:

root@debian11-template:~# systemctl status dnsmasq.service ● dnsmasq.service - dnsmasq - A lightweight DHCP and caching DNS server Loaded: loaded (/lib/systemd/system/dnsmasq.service; enabled; vendor preset: enabled) Active: active (running) since Mon 2022-05-09 00:50:29 CEST; 6s ago Process: 13153 ExecStartPre=/etc/init.d/dnsmasq checkconfig (code=exited, status=0/SUCCESS) Process: 13160 ExecStart=/etc/init.d/dnsmasq systemd-exec (code=exited, status=0/SUCCESS) Process: 13168 ExecStartPost=/etc/init.d/dnsmasq systemd-start-resolvconf (code=exited, status=0/SUCCESS) Main PID: 13167 (dnsmasq) Tasks: 1 (limit: 1129) Memory: 576.0K CPU: 28ms CGroup: /system.slice/dnsmasq.service └─13167 /usr/sbin/dnsmasq -x /run/dnsmasq/dnsmasq.pid -u dnsmasq -7 /etc/dnsmasq.d,.dpkg-dist,.dpkg-old,.dpkg-new --local-service --trust-anchor=.,20326,8,2,e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8e> May 09 00:50:29 debian11-template systemd[1]: Starting dnsmasq - A lightweight DHCP and caching DNS server... May 09 00:50:29 debian11-template dnsmasq[13167]: started, version 2.85 DNS disabled May 09 00:50:29 debian11-template dnsmasq[13167]: compile time options: IPv6 GNU-getopt DBus no-UBus i18n IDN2 DHCP DHCPv6 no-Lua TFTP conntrack ipset auth cryptohash DNSSEC loop-detect inotify dumpfile May 09 00:50:29 debian11-template dnsmasq-dhcp[13167]: DHCP, proxy on subnet 192.168.1.0 May 09 00:50:29 debian11-template dnsmasq-tftp[13167]: TFTP root is /tftpboot May 09 00:50:29 debian11-template systemd[1]: Started dnsmasq - A lightweight DHCP and caching DNS server. root@debian11-template:~# cat /etc/dnsmasq.conf port=0 log-dhcp dhcp-range=192.168.1.0,proxy dhcp-boot=pxelinux.0 pxe-service=x86PC,'Network Boot',pxelinux enable-tftp tftp-root=/tftpboot root@debian11-template:~# ss -tlnp|grep dnsm root@debian11-template:~# ss -tlnp|grep dns root@debian11-template:~# ss -ulnp|grep dns UNCONN 0 0 0.0.0.0:4011 0.0.0.0:* users:(("dnsmasq",pid=13167,fd=5)) UNCONN 0 0 0.0.0.0:67 0.0.0.0:* users:(("dnsmasq",pid=13167,fd=4)) UNCONN 0 0 0.0.0.0:69 0.0.0.0:* users:(("dnsmasq",pid=13167,fd=7)) UNCONN 0 0 [::]:69 [::]:* users:(("dnsmasq",pid=13167,fd=8))

Please know that dhcp-range was adjusted to fit my IP subnet.

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The problem is, from the error, that you already have soemthing listening on that IP:PORT. Since you have systemd and dnsmasq does DNS, most likely systemd-resolved is there using port 53 UDP that dnsmasq is trying to bind to. I really really hate how systemd breaks the designs and tries to be be-all-do-all. Right rant over.

Use netstat -lnp to see what is listening on tftp or dns ports. Then choose to replace that service with dnsmasq. If it’s systemd-resolved, you can just disable that sucker and configure DNS in /etc/resolv.conf

If you don’t have netstat, you can use ss.

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