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David Lee
Asked: 2020-07-06 20:30:49 +0800 CST

why a modules is loaded into kernel even if the config option is m

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the config option which determines whether the udp_tunnel module is compiled into the kernel is CONFIG_NET_UDP_TUNNEL. And the CONFIG_NET_UDP_TUNNEL in .config of Ubuntu is M, which should not be loaded into kernel automatically. But the result below shows that the udp_tunnel is loaded into kernel, which is confused to me.

$ modinfo udp_tunnel
filename:       /lib/modules/5.3.0-51-generic/kernel/net/ipv4/udp_tunnel.ko
license:        GPL
srcversion:     0A315BA6124B0664F4D23FB
depends:        
retpoline:      Y
intree:         Y
name:           udp_tunnel
vermagic:       5.3.0-51-generic SMP mod_unload 
signat:         PKCS#7
signer:         
sig_key:        
sig_hashalgo:   md4

$ echo $?
0

shows the modules udp_tunnel is loaded into the kernel and

kernel

1 Answers

  1. Looking up the information about a module does not mean it is loaded. modinfo will look in /lib/modules/version for it also.

    If you want to know if it is loaded then use lsmod. Example:

    doug@s18:/boot$ lsmod | grep udp
xt_tcpudp              20480  9
x_tables               45056  9 xt_conntrack,iptable_filter,xt_tcpudp,xt_CHECKSUM,ip6_tables,ipt_REJECT,ip_tables,xt_MASQUERADE,iptable_mangle

    Now if the module is force loaded:

    doug@s18:/boot$ sudo modprobe udp_tunnel
[sudo] password for doug:
doug@s18:/boot$ lsmod | grep udp
udp_tunnel             16384  0
xt_tcpudp              20480  9
x_tables               45056  9 xt_conntrack,iptable_filter,xt_tcpudp,xt_CHECKSUM,ip6_tables,ipt_REJECT,ip_tables,xt_MASQUERADE,iptable_mangle
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