On 07.03.2018 16:05, Mark Reynolds wrote:

Hello,

So I am running into two issues with file watching on cockpit-151-2

[1]  The first one appears to be a permissions issue.  So I am trying to
watch a file that the Cockpit user does have immediate permissions to,
but the Cockpit user does have sudo rights.  When I try to watch the
file, I get an error:  "Not permitted to perform this action." - I'm
assuming it's permissions issue because if I watch a file in /tmp it
works fine (I also tried disabling selinux but no luck).

My code:

        var logfile =
cockpit.file("/var/log/dirsrv/slapd-localhost/errors");
        //var logfile = cockpit.file("/tmp/errors");
        errorslog_watch = logfile.watch(function (content, tag, error) {
          $('#errorslog-area').text(content);
          console.log("We should have logged something: (" + content +
") err: " + error);
        });

This generates in console:

    We should have logged something: (null) err: Not permitted to
perform this action.

I'm not 100% sure what that errors means, but is there something what
will invoke sudo on the file access/watching?

I think you want something like:

var logfile = cockpit.file("/tmp/errors", { "superuser": true });

[2]  What I want to do is the equivalent of "tailing" a log file, and I
would like to use Cockpit's file watching functionality to do this. 
However, when the log file changes the entire file content is returned. 
Our log files can grow up to 100mb.  Is there a way to only return the
last N lines of a file when it changes without loading the entire
content into memory?

I'd suggest just running the "tail" command:

var proc = cockpit.spawn(["tail", "-f", "/tmp/errors"], { "superuser":
true });

And then using proc.stream() to get the data.

Hope that helps,

Stef

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