I am running Ubuntu server 14.04.3.
I have smcroute installed – Version 0.95, Build 130523. When I attempt to start the daemon I get the error message: ERRO: addVIF, out of VIF space;, this happens after it attempts to add the 33rd network interface of my machine.
Looking in mroute.h in /usr/include/linux/ folder, I saw a MAXVIFS defined as 32, so I upped it to 100 and saved the file.
After a reboot I can still see the 32 limit being imposed, but the file still states 100. How can I force the OS to read from this file?
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Answer
First, you need to understand why that number is 32. And that comes from the line below where MAXVIFS is defined:
typedef unsigned long vifbitmap_t; /* User mode code depends on this lot */
On a 32bit machine (which is where this ancient crap started), that would a 32bit register. When you want a bitmap bigger than a register, things get messy. (see also: the FD_SET() macros) 64 is safe on a 64bit machine.
To increase the number of interfaces, you need to change both the userspace define (the file you changed) AND the define in the kernel (include/linux/mroute.h within the kernel source.) Then, rebuild your kernel and every userspace application that messes with multicast.
** Changing that define alters an ioctl data structure. **