How can I increase the value of somaxconn?
I can check its value by cat /proc/sys/net/core/somaxconn,
is it OK if I change it simply by echo 1024 > /proc/sys/net/core/somaxconn?
Yes. Alternatively, you can use:
sysctl -w net.core.somaxconn=1024
Add net.core.somaxconn=1024 to /etc/sysctl.conf for it to become permanent (be reapplied after booting).
yes /proc/sys/net/core/somaxconn is writable if you have the permissions to do so.