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# Erlang Top

## Introduction

Erlang Top, `etop`, is a tool for presenting information about Erlang processes
similar to the information presented by `top` in UNIX.

## Getting Started

Start Erlang Top in either of the following ways:

- Use script `etop`.
- Use batch file `etop.bat`, for example, `etop -node tiger@durin`.

## Output

The output from Erlang Top is as follows:

```text
========================================================================================
 tiger@durin                                                               13:40:32
 Load:  cpu         0               Memory:  total        1997    binary         33
        procs     197                        processes       0    code          173
        runq      135                        atom         1002    ets            95

Pid            Name or Initial Func    Time    Reds  Memory    MsgQ Current Function
----------------------------------------------------------------------------------------
<127.23.0>     code_server                0   59585   78064       0 gen_server:loop/6
<127.21.0>     file_server_2              0   36380   44276       0 gen_server:loop/6
<127.2.0>      erl_prim_loader            0   27962    3740       0 erl_prim_loader:loop
<127.9.0>      kernel_sup                 0    6998    4676       0 gen_server:loop/6
<127.17.0>     net_kernel                62    6018    3136       0 gen_server:loop/6
<127.0.0>      init                       0    4156    4352       0 init:loop/1
<127.16.0>     auth                       0    1765    1264       0 gen_server:loop/6
<127.18.0>     inet_tcp_dist:accept       0     660    1416       0 prim_inet:accept0/2
<127.5.0>      application_controll       0     569    6756       0 gen_server:loop/6
<127.137.0>    net_kernel:do_spawn_       0     553    5840       0 dbg:do_relay_1/1
========================================================================================
```

The header includes some system information:

- **`Load`**

  - **`cpu`** - `Runtime/Wallclock`, that is, the percentage of time where the
    node has been active.

  - **`procs`** - The number of processes on the node.

  - **`runq`** - The number of processes that are ready to run.

- **`Memory`** - The memory allocated by the node in kilobytes.

For each process the following information is presented:

- **`Time`** - The runtime for the process, that is, the time that the process
  has been scheduled in.

- **`Reds`** - The number of reductions executed on the process.

- **`Memory`** - The size of the process in bytes, obtained by a call to
  [`process_info(Pid,memory)`](`process_info/2`).

- **`MsgQ`** - The length of the message queue for the process.

> #### Note {: .info }
>
> _Time_ and _Reds_ can be presented as accumulated values or as values since
> the last update.

## Configuration

All configuration parameters can be set at start by adding `-OptName Value` to
the command line, for example:

```text
% etop -node tiger@durin -setcookie mycookie -lines 15
```

A list of all valid Erlang Top configuration parameters is available in module
`m:etop`.

The parameters `lines`, `interval`, `accumulate`, and `sort` can be changed
during runtime with function `etop:config/2`.

_Example:_

Change configuration parameter `lines` with text-based presentation. Before the
change, 10 lines are presented as follows:

```text
========================================================================================
 tiger@durin                                                               10:12:39
 Load:  cpu         0               Memory:  total        1858    binary         33
        procs     191                        processes       0    code          173
        runq        2                        atom         1002    ets            95

Pid            Name or Initial Func    Time    Reds  Memory    MsgQ Current Function
----------------------------------------------------------------------------------------
<127.23.0>     code_server                0   60350   71176       0 gen_server:loop/6
<127.21.0>     file_server_2              0   36380   44276       0 gen_server:loop/6
<127.2.0>      erl_prim_loader            0   27962    3740       0 erl_prim_loader:loop
<127.17.0>     net_kernel                 0   13808    3916       0 gen_server:loop/6
<127.9.0>      kernel_sup                 0    6998    4676       0 gen_server:loop/6
<127.0.0>      init                       0    4156    4352       0 init:loop/1
<127.18.0>     inet_tcp_dist:accept       0    2196    1416       0 prim_inet:accept0/2
<127.16.0>     auth                       0    1893    1264       0 gen_server:loop/6
<127.43.0>     ddll_server                0     582    3744       0 gen_server:loop/6
<127.5.0>      application_controll       0     569    6756       0 gen_server:loop/6
========================================================================================
```

Function `etop:config/2` is called to change the number of showed lines to 5:

```text
> etop:config(lines,5).
ok
```

After the change, 5 lines are presented as follows:

```text
(etop@durin)2>
========================================================================================
 tiger@durin                                                               10:12:44
 Load:  cpu         0               Memory:  total        1859    binary         33
        procs     192                        processes       0    code          173
        runq        2                        atom         1002    ets            95

Pid            Name or Initial Func    Time    Reds  Memory    MsgQ Current Function
----------------------------------------------------------------------------------------
<127.17.0>     net_kernel               183      70    4092       0 gen_server:loop/6
<127.335.0>    inet_tcp_dist:do_acc     141      22    1856       0 dist_util:con_loop/9
<127.19.0>     net_kernel:ticker/2      155       6    1244       0 net_kernel:ticker1/2
<127.341.0>    net_kernel:do_spawn_       0       0    5840       0 dbg:do_relay_1/1
<127.43.0>     ddll_server                0       0    3744       0 gen_server:loop/6
========================================================================================
```

## Print to File

At any time, the current Erlang Top display can be dumped to a text file with
function `etop:dump/1`.

## Stop

To stop Erlang Top, use function `etop:stop/0`.
