Instead of restarting dnsmasq, try deleting the log file and telling
dnsmasq to open a new one.
rm /var/log/dnsmasq.log
killall -USR2 dnsmasq
If that also causes the memory usage to fall, then you are being led
astray by a the lg file being memory mapped. If the memeory usage
doesn't fall, there might be a real memory leak.
Cheers,
Simon.
On 14/04/2025 17:55, Nitesh Divecha wrote:
Hello Simon,
Thank you for your feedback.
Yes, when I turn on --log-facility=/var/log/dnsmasq.log, I see memory-size
growing.
# systemctl status dnsmasq
* dnsmasq.service - DNS forwarder and DHCP server
Loaded: loaded (/lib/systemd/system/dnsmasq.service; enabled; vendor
preset: enabled)
Drop-In: /etc/systemd/system/dnsmasq.service.d
`-override.conf
Active: active (running) since Sat 2025-04-12 21:27:30 UTC; 15h ago
Process: 427 ExecStartPre=/usr/bin/dnsmasq --test (code=exited,
status=0/SUCCESS)
Process: 434 ExecStart=/usr/bin/dnsmasq -x /run/dnsmasq.pid -7
/etc/NetworkManager/dnsmasq.d --local-service (code=exited, status=0/SUCCESS)
Main PID: 437 (dnsmasq)
Tasks: 1 (limit: 1042)
Memory: 16.3M
CGroup: /system.slice/dnsmasq.service
`- 437 /usr/bin/dnsmasq -x /run/dnsmasq.pid -7
/etc/NetworkManager/dnsmasq.d --local-service
# ls -lah /var/log/dnsmasq.log
-rw-rw---- 1 nobody root 16M Apr 13 13:05 /var/log/dnsmasq.log
And if I restart the service it will reset the log file and memory-size will go
down.
# systemctl status dnsmasq --no-pager
● dnsmasq.service - DNS forwarder and DHCP server
Loaded: loaded (/lib/systemd/system/dnsmasq.service; enabled; vendor
preset: enabled)
Drop-In: /etc/systemd/system/dnsmasq.service.d
└─override.conf
Active: active (running) since Mon 2025-04-14 16:08:27 UTC; 43min ago
Process: 2238 ExecStartPre=/usr/bin/dnsmasq --test (code=exited,
status=0/SUCCESS)
Process: 2239 ExecStart=/usr/bin/dnsmasq -x /run/dnsmasq.pid -7
/etc/NetworkManager/dnsmasq.d --bind-dynamic --local-service
--listen-address=127.0.0.1 --listen-address=192.0.2.2 (code=exited,
status=0/SUCCESS)
Main PID: 2242 (dnsmasq)
Tasks: 1 (limit: 1042)
Memory: 1.3M
CGroup: /system.slice/dnsmasq.service
└─ 2242 /usr/bin/dnsmasq -x /run/dnsmasq.pid -7
/etc/NetworkManager/dnsmasq.d --bind-dynamic --local-service
--listen-address=127.0.0.1 --listen-address=192.0.2.2
Apr 14 16:08:27 2026240055 systemd[1]: Starting DNS forwarder and DHCP server...
Apr 14 16:08:27 2026240055 dnsmasq[2238]: dnsmasq: syntax check OK.
Apr 14 16:08:27 2026240055 systemd[1]: Started DNS forwarder and DHCP server.
# ls -lah /var/log/dnsmasq.log
-rw-rw---- 1 nobody root 1.2M Apr 14 16:52 /var/log/dnsmasq.log
Cheers,
Nitesh
On Apr 14, 2025, at 10:48 AM, Simon Kelley <si...@thekelleys.org.uk> wrote:
On 4/13/25 13:45, Nitesh Divecha via Dnsmasq-discuss wrote:
Hi all,
I'm using dnsmasq version 2.90 in an embedded Linux project based on the Yocto
Project (kirkstone branch). The recipe in use is from the OpenEmbedded
meta-networking layer: https://layers.openembedded.org/layerindex/recipe/304520/
I've observed that dnsmasq memory usage steadily increases over time, even
under light DNS query loads. For example:
- On boot: ~1.1 MB
- After 1 hour: ~3.3 MB
- After ~14 hours: ~15.3 MB
Relevant configuration (via NetworkManager):
# cat /etc/NetworkManager/dnsmasq.d/dnsmasq-dns.conf
no-negcache
stop-dns-rebind
server=8.8.8.8
server=1.1.1.1
all-servers
log-queries
log-facility=/var/log/dnsmasq.log
I noticed that the `/var/log/dnsmasq.log` file grows continuously (currently
~15M), and suspect that this may be contributing to memory growth — either due
to internal buffering or cumulative logging state.
My questions:
1. Is this memory growth expected when `log-queries` is enabled with
`log-facility`?
2. Does `dnsmasq` buffer log output internally, or are there known issues with
memory not being reclaimed after prolonged logging?
3. Are there recommended best practices for logging in long-running embedded
environments to avoid this kind of memory usage?
Any suggestions or insights would be greatly appreciated.
Thanks in advance,
Cheers,
Nitesh
Do you only see this memory-size growth when logging to a file? It's possible
that there's a memory leak elsewhere, but unlikely that one that big could have
been undetected until now.
It's possible that the libc in use is memory-mapping the log file. Dnsmasq uses
very standard open() and write() calls, but it's up to the libc how it
implements that. Memory-mapping the file and converting write() calls to memory
writes would be a legitimate thing to do. In this case some measures of the
process's memory usage would increase, but the actual physical RAM usage would
not - long untouched pages will be written out to the filesystem and the RAM
freed for reuse, just like swapping.
Dnsmasq allows log-file rotation in the conventional way. The simplest thing to
do is to delete the log file and then send the dnsmasq process SIGUSR2. That
makes dnsmasq close and reopen the file. The close removes the last reference
to the deleted file and its disk storage is freed-up. The re-open creates a new
log file which begins empty. Real logfile rotation renames the live file
instead of deleting it, and only deletes old logfiles after a few days: see man
logrotate for details on that.
Cheers,
Simon.
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