trickle: throttle all programs: works for statically linked executables?

Question

I want to use trickle on Raspbian.

It seems it can be used when running an executable as follows:

• trickle -u {up} -d {down} {program}

And it can also be used for all applications. e.g.:

• trickled -d 50 -u 10

The man page says that the first cannot be used on statically linked executables. So my question is, will the second usage example apply to all programs, whether they are statically linked or not?

Thanks

Answer 1

trickled uses the same technique to limit bandwidth as trickle. It just listens on a UNIX domain socket in /tmp for other trickle processes. When another trickle process starts up, it will ask trickled (if it is running) for the global settings, and set these as defaults, unless it has individual overrides for that specific instance of trickle.

A fully statically linked executable (meaning that everything, including libc, is statically compiled into the binary) can't be used with a userspace process like trickle. What eventually happens with a statically linked executable is that it makes system calls directly into the Linux kernel's stable user<->kernel Application Binary Interface (ABI). It does not attempt to load any libraries within /lib, /usr/lib, /usr/local/lib, etc. to resolve symbols.

The magic of trickle is that it effectively injects custom code into processes that do dynamically load the C library from the system. Processes that don't, or processes that are setuid root, can't have their code modified in this way.

To truly control all processes on the system, this level of bandwidth limiting would need to be done in the kernel itself.

There are a few kernel implementations, both old and new, of traffic shaping functionality (traffic shaping is the generalized term for bandwidth limiting, and it generally means modifying the timing or scheduling of packets) in the Linux kernel itself, and these are much more reliable. here is a more recent example based on the nf framework, which is slated to replace iptables as the layer 3 policy and control stack for modern Linux.