> ## Content Index > Fetch the complete content index at: https://til.codes/llms.txt > Use this file to discover other available public pages before exploring further. # Tracing in Elixir/Erlang using dbg trips and tricks. - URL: https://til.codes/tracing-in-elixir-erlang-using-dbg-trips-and-tricks/ - Published: 2020-04-10T17:35:52.000Z - Updated: 2020-04-11T13:39:52.000Z - Description: Tips and tricks for tracing in elixir/erlang using dbg module and some helper functions. - Author: Manu Ajith - Tags: elixir, erlang, tracing, dbg, #Import 2024-07-13 21:01 For context, I was trying to debug/understand a new codebase and wanted to do some tracing so that I could better understand the flow, so I started tracing these functions using the `dbg` module from Erlang. But one of the common cons of the dbg module is the documentation of the functions, and odd function names ``` iex(1)> :dbg. c/3 c/4 cn/1 ctp/0 ctp/1 ctp/2 ctp/3 ctpe/1 ctpg/0 ctpg/1 ctpg/2 ctpg/3 ctpl/0 ctpl/1 ctpl/2 ctpl/3 deliver_and_flush/1 dhandler/2 dtp/0 dtp/1 erlang_trace/3 flush_trace_port/0 flush_trace_port/1 fun2ms/1 get_info/0 get_tracer/0 get_tracer/1 h/0 h/1 i/0 ln/0 ltp/0 match_0_9/1 match_front/2 match_rear/2 n/1 p/1 p/2 rtp/1 start/0 stop/0 stop_clear/0 stop_trace_client/1 tp/2 tp/3 tp/4 tpe/2 tpl/2 tpl/3 tpl/4 trace_client/2 trace_client/3 trace_port/2 trace_port_control/1 trace_port_control/2 tracer/0 tracer/2 tracer/3 transform_flags/1 wrap_postsort/1 wrap_presort/2 wrap_sort/2 wrap_sortfix/2 wtp/1 ``` And without having the documentation in one hand, it would be impossible to remember all these function names and their arguments and options. I always wondered whether there would be a simpler way to do this. Of-course there are thin elixir wrappers around it which provide a much more friendly DSL, but it would mean adding another dependency. There are also other libraries like `recon`, `redbug`, `xprof` etc, but all has the same caveats. So after searching for a while, I came across this stack overflow [post](https://stackoverflow.com/questions/1954894/using-trace-and-dbg-in-erlang/2831375?ref=til.codes#2831375) where it provides a simple Erlang wrapper module with a more friendly function names. Source code available here: [saleyn/utilErlang utility modules. Contribute to saleyn/util development by creating an account on GitHub.![](https://github.githubassets.com/favicons/favicon.svg)GitHubsaleyn![](https://avatars1.githubusercontent.com/u/272543?s=400&v=4)](https://github.com/saleyn/util/blob/master/src/user%5Fdefault.erl?ref=til.codes) That was exactly the thing that I was looking for: ``` iex(5)> :dbg_tracer.help ** shell internal commands ** b() -- display all variable bindings e(N) -- repeat the expression in query f() -- forget all variable bindings f(X) -- forget the binding of variable X h() -- history history(N) -- set how many previous commands to keep results(N) -- set how many previous command results to keep catch_exception(B) -- how exceptions are handled v(N) -- use the value of query rd(R,D) -- define a record rf() -- remove all record information rf(R) -- remove record information about R rl() -- display all record information rl(R) -- display record information about R rp(Term) -- display Term using the shell's record information rr(File) -- read record information from File (wildcards allowed) rr(F,R) -- read selected record information from file(s) rr(F,R,O) -- read selected record information with options ** commands in module c ** bt(Pid) -- stack backtrace for a process c(Mod) -- compile and load module or file cd(Dir) -- change working directory flush() -- flush any messages sent to the shell help() -- help info i() -- information about the system ni() -- information about the networked system i(X,Y,Z) -- information about pid l(Module) -- load or reload module lm() -- load all modified modules lc([File]) -- compile a list of Erlang modules ls() -- list files in the current directory ls(Dir) -- list files in directory m() -- which modules are loaded m(Mod) -- information about module mm() -- list all modified modules memory() -- memory allocation information memory(T) -- memory allocation information of type nc(File) -- compile and load code in on all nodes nl(Module) -- load module on all nodes pid(X,Y,Z) -- convert X,Y,Z to a Pid pwd() -- print working directory q() -- quit - shorthand for init:stop() regs() -- information about registered processes nregs() -- information about all registered processes uptime() -- print node uptime xm(M) -- cross reference check a module y(File) -- generate a Yecc parser ** commands in module i (interpreter interface) ** ih() -- print help for the i module ** user extended commands ** dbgtc(File) -- use dbg:trace_client() to read data from File dbgon(M) -- enable dbg tracer on all funs in module M dbgon(M,Fun) -- enable dbg tracer for module M and function F dbgon(M,File) -- enable dbg tracer for module M and log to File dbgadd(M) -- enable call tracer for module M dbgadd(M,F) -- enable call tracer for function M:F dbgdel(M) -- disable call tracer for module M dbgdel(M,F) -- disable call tracer for function M:F dbgoff() -- disable dbg tracer (calls dbg:stop/0) l() -- load all changed modules la() -- load all modules mm() -- list modified modules ``` Pro tip: You can add it to your `.iex.exs` file if you need to be using the module quite often and in multiple projects. Copy the code into `dbg_tracer.erl` and in your home directory, and add the following to `.iex.exs` so that it compiles the erlang module and make it available. ``` c("dbg_tracer.erl") ``` Hope that helps someone. Cheers. References: [Using trace and dbg in ErlangI am trying to start using erlang:trace/3 and the dbg module to trace the behaviour of a live production system without taking the server down. The documentation is opaque (to put it mildly) and t...![](https://cdn.sstatic.net/Sites/stackoverflow/img/apple-touch-icon.png?v=c78bd457575a)Stack OverflowGordon Guthrie![](https://cdn.sstatic.net/Sites/stackoverflow/img/apple-touch-icon@2.png?v=73d79a89bded)](https://stackoverflow.com/questions/1954894/using-trace-and-dbg-in-erlang/2831375?ref=til.codes#2831375) [saleyn/utilErlang utility modules. Contribute to saleyn/util development by creating an account on GitHub.![](https://github.githubassets.com/favicons/favicon.svg)GitHubsaleyn![](https://avatars1.githubusercontent.com/u/272543?s=400&v=4)](https://github.com/saleyn/util/blob/master/src/user%5Fdefault.erl?ref=til.codes)