how to save mnesia:info() output?
I use remote sh in unix screen and can't to scroll window
Here's a function that you can put in the user_default.erl module on the remote node:
out(Fun, File) ->
G = erlang:group_leader(),
{ok, FD} = file:open(File, [write]),
erlang:group_leader(FD, self()),
Fun(),
erlang:group_leader(G, self()),
file:close(FD).
Then, you can do the following (after recompiling and loading user_default):
1> out(fun () -> mnesia:info() end, "mnesia_info.txt").
Or, just cut-and paste the following into the shell:
F = fun (Fun, File) ->
G = erlang:group_leader(),
{ok, FD} = file:open(File, [write]),
erlang:group_leader(FD, self()),
Fun(),
erlang:group_leader(G, self()),
file:close(FD)
end,
F(fun () -> mnesia:info() end, "mnesia_info.txt").
In cases where you are situated at a terminal without scrolling (if you are on a xterm and see no scrollbar simply switch it on) a tool very useful is screen: it provides virtual vt100 termials, you can switch between terminals even detach from it and come back later (nice for long running programs on remote serversthat need the occasional interaction).
And you can log transcripts to a file and scroll in the output of the virtual terminal.
If you are on a Unix like System you will probably be able to just install a pre-built package, if all else fails you can always pick up the source and build it yourself.
Also look at this article for other solutions.
If you are not able to install screen on the system, a simple but not very comfortable hack that only uses Unix built-in stuff is:
Start erlang shell with tee(1) to redirect the output:
$ erl | tee output.log
Eshell V5.7.5 (abort with ^G)
1> mnesia:info().
===> System info in version {mnesia_not_loaded,nonode#nohost,
{1301,742014,571300}}, debug level = none <===
opt_disc. Directory "/usr/home/peer/Mnesia.nonode#nohost" is NOT used.
use fallback at restart = false
running db nodes = []
stopped db nodes = [nonode#nohost]
ok
2>
Its a bit hard to get out of the shell (you probably have to type ^D to end the input file) but then you have the tty output in the file:
$ cat output.log
Eshell V5.7.5 (abort with ^G)
1> ===> System info in version {mnesia_not_loaded,nonode#nohost,
{1301,742335,572797}}, debug level = none <===
...
I believe you cant. See system_info(all).
Convert to a string:
S = io_lib:format("~p~n", [mnesia:info()]).
Then write it to disk.
Related
I want to run an external script and get the PID of the process (once it starts) from my erlang program. Later, I will want to send TERM signal to that PID from erlang code. How do I do it?
I tried this
P = os:cmd("myscript &"),
io:format("Pid = ~s ~n",[P]).
It starts the script in background as expected, but I dont get the PID.
Update
I made the below script (loop.pl) for testing:
while(1){
sleep 1;
}
Then tried to spawn the script using open_port. The script runs OK. But, erlang:port_info/2 troughs exception:
2> Port = open_port({spawn, "perl loop.pl"}, []).
#Port<0.504>
3> {os_pid, OsPid} = erlang:port_info(Port, os_pid).
** exception error: bad argument
in function erlang:port_info/2
called as erlang:port_info(#Port<0.504>,os_pid)
I checked the script is running:
$ ps -ef | grep loop.pl
root 10357 10130 0 17:35 ? 00:00:00 perl loop.pl
You can open a port using spawn or spawn_executable, and then use erlang:port_info/2 to get its OS process ID:
1> Port = open_port({spawn, "myscript"}, PortOptions).
#Port<0.530>
2> {os_pid, OsPid} = erlang:port_info(Port, os_pid).
{os_pid,91270}
3> os:cmd("kill " ++ integer_to_list(OsPid)).
[]
Set PortOptions as appropriate for your use case.
As the last line above shows, you can use os:cmd/1 to kill the process if you wish.
I want to copy files from one server(Say A) to other(Say B).Scenerio is->User sends me a file(video,zip or photo) in binary.I write this to /var/www/myfolder of A.Now in next step i want this to be copied at B.I used os:cmd(scp ----) command.But it gives error like->
Permission denied, please try again.
Permission denied, please try again.
Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).
I think it is asking for password of B.How can i configure password in scp command or is there any other method to do this in erlang?
You can use Erlang File I/O if you have both servers connected using erlang distribution protocol. (You can do it over TCP or UDP or any other networking as well but it is more complicated).
Let's demonstrate it using two "servers" running on the same machine (it works same over a network, but you have to connect them properly). First we make directory for each server and content of file foo to transfer:
$ mkdir a b
$ echo Hello World > a/foo
Let's start two servers each in a different directory:
$ cd a
a$ erl -sname a
Erlang/OTP 18 [erts-7.0] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V7.0 (abort with ^G)
(a#hynek-notebook)1>
and the second server in a different console:
$ cd b
b$ erl -sname b
Erlang/OTP 18 [erts-7.0] [source] [64-bit] [smp:4:4] [async-threads:10] [hipe] [kernel-poll:false]
Eshell V7.0 (abort with ^G)
(b#hynek-notebook)1>
Now we check there is nothing on the b server yet:
(b#hynek-notebook)1> ls().
ok
(b#hynek-notebook)2>
Now we can connect nodes, check if they are connected and read the file foo.
(a#hynek-notebook)1> net_kernel:connect('b#hynek-notebook').
true
(a#hynek-notebook)2> net_adm:ping('b#hynek-notebook').
pong
(a#hynek-notebook)3> ls().
foo
ok
(a#hynek-notebook)4> {ok, Bin} = file:read_file("foo").
{ok,<<"Hello World\n">>}
(a#hynek-notebook)5>
And write file to server b using rpc:call/4:
(a#hynek-notebook)5> rpc:call('b#hynek-notebook', file, write_file, ["bar", Bin]).
ok
(a#hynek-notebook)6>
Check the result on the server b:
(b#hynek-notebook)2> ls().
bar
ok
(b#hynek-notebook)3> {ok, Bin} = file:read_file("bar").
{ok,<<"Hello World\n">>}
(b#hynek-notebook)4>
For bigger files, you should not transfer a whole file in the one big binary. Unfortunately, you need at least some code support from sending or receiving side. You can transfer file handler from one node to another but the process which calls file:open/2 has to keep running. It is reason you can't just use {ok, FH} = rpc:call(Node, file, open, [FN, [write]]). It's a bummer. One way is to make a very simple server which opens a file and keeps running.
(b#hynek-notebook)4> Self = self().
<0.40.0>
(b#hynek-notebook)5> F = fun() -> Self ! file:open("baz", [write]), receive close -> ok end end.
#Fun<erl_eval.20.54118792>
(b#hynek-notebook)6> FS = spawn_link('a#hynek-notebook', F).
<7329.48.0>
(b#hynek-notebook)7> {ok, FH} = receive X -> X end.
{ok,<7329.49.0>}
(b#hynek-notebook)8> file:write(FH, Bin).
ok
(b#hynek-notebook)9> FS ! close.
close
(b#hynek-notebook)10>
And we expect file baz with proper content on the server a:
(a#hynek-notebook)6> ls().
baz foo
ok
(a#hynek-notebook)7> {ok, _} = file:read_file("baz").
{ok,<<"Hello World\n">>}
(a#hynek-notebook)8>
The other option is to write a server which will receive blocks and write them instead of sending a file handler. And there are many other options how to do it using direct TCP connection using HTTP or your own protocol and using file:send_file/2,5 and many other ways.
Facing problem with slave:start/2 in lion OS, so I have to try another direction "start common node with os:cmd automatically" in erlang shell.
One way is by command directly, and another way is through bash file. But both way faces the same problem. If can't start automatically, I have to start node manually everytime.
Eshell V5.9 (abort with ^G)
(emacs#yus-iMac.local)1> os:cmd("erl -name abcd").
"Eshell V5.9 (abort with ^G)\n(abcd#yus-iMac.local)1> *** Terminating erlang ('abcd#yus-iMac.local')\n"
(emacs#yus-iMac.local)3> os:cmd("~/Documents/Project/node_start").
"Eshell V5.9 (abort with ^G)\n(abc#yus-iMac.local)1> *** Terminating erlang ('abc#yus-iMac.local')\n"
The bash file content is as follows:
#/bin/sh
erl -name abc
Not that I'm really fond of this approach, but to make the above work you should pass the "detached" parameter to the 'erl' command:
erl -name foo
1> os:cmd("erl -name bar -detached").
[]
2> net_adm:ping('bar#pigeon.local').
pong
3> nodes().
['bar#pigeon.local']
Reading from the doc:
-detached
Starts the Erlang runtime system detached from the system console. Useful for running daemons and backgrounds processes. Implies
-noinput.
When I call open_port without exit_status in the example below it is unusable:
Eshell V5.7.5 (abort with ^G)
1> P = open_port({spawn, "cat >bar"}, [stream, use_stdio]).
#Port<0.498>
2> port_command(P, "hello\n").
** exception error: bad argument
in function port_command/2
called as port_command(#Port<0.498>,"hello\n")
But when I just add exit_status and leave everything the same it works:
Eshell V5.7.5 (abort with ^G)
1> P = open_port({spawn, "cat >bar"}, [stream, use_stdio, exit_status]).
#Port<0.498>
2> port_command(P, "hello\n").
true
From the documentation I don't understand the difference in behaviour.
When you redirect output in a file in cat >bar command shell closes stdout and Erlang just closes the port in this case because ports try to consume command output by default and close on eof. The right way to fix it is to use out option as butter71 already suggested. Options like out, exit_status, error_to_stdout tell ports to not bother about stdout.
try setting the port for output only:
P = open_port({spawn, "cat >bar"}, [stream, use_stdio, out]).
port_command(P, "hello\n").
my guess is that erlang is unhappy because you redirected the command's stdout.
I have a file .erlang in the current dir I run erl shell that compiles a few modules.
Is there way to re run this file from the Erlang shell.
I run erl I get the shell 1> and from there run like run_file(".erlang") and this file execute the instructions in the current shell and load the env.
The file looks like
compile:file(file1).
compile:file(file2).
compile:file(file3).
...
You're looking for file:eval/1.
Given a .erlang with this content:
io:format("Hello world!~n").
You get:
Eshell V5.7.5 (abort with ^G)
1> file:eval(".erlang").
Hello, world!
ok
You might want to look into escript.