I have checked about the function of "-n" --
"Displays active TCP connections, however, addresses and port numbers are expressed numerically and no attempt is made to determine names."
But I can't see why "-n" can make netstat exit immediately?
From a quick check, I don't see the same description for the "-n" option as you do, and it doesn't make netstat run continuously.
As you didn't specify the version and exact command you are using, I tried both the version that comes with RH7.6 (net-tools 2.10-alpha) and the latest from source code (net-tools 3.14-alpha). The net-tools source code can be found in github [1].
As I couldn't find the exact option you describe, I tried all flags (without combinations) that don't require an argument. As far as I can tell the only options that cause netstat to not exit immediately are '-g' and '-c'. '-c' makes sense as it is the flag for running netstat continuously. For '-g' it isn't as obvious as the continuous behavior is coming from reading the /proc/net/igmp and /proc/net/igmp6 files line-by-line. The first file is read quickly but the igmp6 file takes much longer (1 line per ~1 sec). The '-g' option isn't really continuous, but just takes a lot of time to finish.
From the code, the only reason for continuous execution is (appears 4 times in the code):
if (i || !flag_cnt)
break;
wait_continous();
'i' is a return code from a function and the 'break' command is to break from an infinite for loop, so basically the code will run continuously only if flag_cnt is set (only happens when '-c' is provided) and there were no errors with previous commands.
For the specific issue above there could be a few reasons:
The option involves reading from a file and it takes very long time to finish, but it is not really continuous.
There's a correlation between the given option and flag_cnt, which cause flag_cnt to be set.
There's a call to wait_continous() which doesn't follow the condition above.
As I said, I couldn't reproduce the issue in the original question, nor could I find any flag with the description above. Also, non of the flags besides '-c' caused netstat to run continuously.
If you still want to figure this out I suggest you take a look at your code, or at least specify the net-tools version you use. The kernel version is also important as some code would be compiled-out due to missing kernel support.
[1] https://github.com/ecki/net-tools
Related
I am a beginner to programming. I am trying to run a simulation of a combustion chamber using reactingFoam.
I have modified the counterflow2D tutorial.
For those who maybe don't know OpenFOAM, it is a programme built in C++ but it does not require C++ programming, just well-defining the variables in the files needed.
In one of my first tries I have made a very simple model but since I wanted to check it very well I set it to 60 seconds with a 1e-6 timestep.
My computer is not very powerful so it took me for a day aprox. (by this I mean I'd like to find a solution rather than repeating the simulation).
I executed the solver reactingFOAM using 4 processors in parallel using
mpirun -np 4 reactingFOAM -parallel > log
The log does not show any evidence of error.
The problem is that when I use reconstructPar it works perfectly but then I try to watch the results with paraFoam and this error is shown:
From function bool Foam::IOobject::readHeader(Foam::Istream&)
in file db/IOobject/IOobjectReadHeader.C at line 88
Reading "mypath/constant/reactions" at line 1
First token could not be read or is not the keyword 'FoamFile'
I have read that maybe some files are empty when they are not supposed to be so, but I have not found that problem.
My 'reactions' file have not been modified from the tutorial and has always worked.
edit:
Sorry for the vague question. I have modified it a bit.
A typical OpenFOAM dictionary file always contains a Foam::Istream named FoamFile. An example from a typical system/controlDict file can be seen below:
FoamFile
{
version 2.0;
format ascii;
class dictionary;
location "system";
object controlDict;
}
During the construction of the dictionary header, if this Istream is absent, OpenFOAM ceases its operation by raising an error message that you have experienced:
First token could not be read or is not the keyword 'FoamFile'
The benefit of the header is possibly to contribute OpenFOAM's abstraction mechanisms, which would be difficult otherwise.
As mentioned in the comments, adding the header entity almost always solves this problem.
I'm getting this on the console in a QML app:
QFont::setPointSizeF: Point size <= 0 (0.000000), must be greater than 0
The app is not crashing so I can't use the debugger to get a backtrace for the exception. How do I see where the error originates from?
If you know the function the warning occurs in (in this case, QFont::setPointSizeF()), you can put a breakpoint there. Following the stack trace will lead you to the code that calls that function.
If the warning doesn't include the name of the function and you have the source code available, use git grep with part of the warning to get an idea of where it comes from. This approach can be a bit of trial and error, as the code may span more than one line, etc, and so you might have to try different parts of the string.
If the warning doesn't include the name of the function, you don't have the source code available and/or you don't like the previous approach, use the QT_MESSAGE_PATTERN environment variable:
QT_MESSAGE_PATTERN="%{function}: %{message}"
For the full list of variables at your disposal, see the qSetMessagePattern() docs:
%{appname} - QCoreApplication::applicationName()
%{category} - Logging category
%{file} - Path to source file
%{function} - Function
%{line} - Line in source file
%{message} - The actual message
%{pid} - QCoreApplication::applicationPid()
%{threadid} - The system-wide ID of current thread (if it can be obtained)
%{qthreadptr} - A pointer to the current QThread (result of QThread::currentThread())
%{type} - "debug", "warning", "critical" or "fatal"
%{time process} - time of the message, in seconds since the process started (the token "process" is literal)
%{time boot} - the time of the message, in seconds since the system boot if that can be determined (the token "boot" is literal). If the time since boot could not be obtained, the output is indeterminate (see QElapsedTimer::msecsSinceReference()).
%{time [format]} - system time when the message occurred, formatted by passing the format to QDateTime::toString(). If the format is not specified, the format of Qt::ISODate is used.
%{backtrace [depth=N] [separator="..."]} - A backtrace with the number of frames specified by the optional depth parameter (defaults to 5), and separated by the optional separator parameter (defaults to "|"). This expansion is available only on some platforms (currently only platfoms using glibc). Names are only known for exported functions. If you want to see the name of every function in your application, use QMAKE_LFLAGS += -rdynamic. When reading backtraces, take into account that frames might be missing due to inlining or tail call optimization.
On an unrelated note, the %{time [format]} placeholder is quite useful to quickly "profile" code by qDebug()ing before and after it.
I think you can use qInstallMessageHandler (Qt5) or qInstallMsgHandler (Qt4) to specify a callback which will intercept all qDebug() / qInfo() / etc. messages (example code is in the link). Then you can just add a breakpoint in this callback function and get a nice callstack.
Aside from the obvious, searching your code for calls to setPointSize[F], you can try the following depending on your environment (which you didn't disclose):
If you have the debugging symbols of the Qt libs installed and are using a decent debugger, you can set a conditional breakpoint on the first line in QFont::setPointSizeF() with the condition set to pointSize <= 0. Even if conditional breakpoints don't work you should still be able to set one and step through every call until you've found the culprit.
On Linux there's the tool ltrace which displays all calls of a binary into shared libs, and I suppose there's something similar in the M$ VS toolbox. You can grep the output for calls to setPointSize directly, but of course this won't work for calls within the lib itself (which I guess could be the case when it handles the QML internally).
Here is a basic script with getopt command and assigned variables.
If someone were to type in
MyScript -a
with no words or numbers added after the -a, then an error message would pop up! The same happens if you replace -a with any other assigned variables. If I wanted no error message to appear, how would I go about doing this?
Hints/advice is preferred over a simply strict answer!
From the bash manual:
getopts can report errors in two ways. If the first character of optstring is a colon, silent error reporting is used. In normal operation diagnostic messages are printed when invalid options or missing option arguments are encountered. If the variable OPTERR is set to 0, no error messages will be displayed, even if the first character of optstring is not a colon.
Since you tag the question with Unix and don't mention bash, you may or may not be so lucky, but the answer is to read the manual page carefully.
Is it possible to graph the query resolution time of bind9 in munin?
I know there is a way to graph it in a unbound server, is it already done in bind? If not how do I start writing a munin plugin for that? I'm getting stats from http://127.0.0.1:8053/ in the bind9 server.
I don't believe that "query time" is a function of BIND. About the only time that I see that value (with individual lookups) is when using dig. If you're willing to use that, the following might be a good starting point:
#!/bin/sh
case $1 in
config)
cat <<'EOM'
graph_title Red Hat Query Time
graph_vlabel time
time.label msec
EOM
exit 0;;
esac
echo -n "time.value "
dig www.redhat.com|grep Query|cut -d':' -f2|cut -d\ -f2
Note that there's two spaces after the "-d\" in the second cut statement. If you save the above as "querytime" and run it at the command line, output should look something like:
root#pi1:~# ./querytime
time.value 189
root#pi1:~# ./querytime config
graph_title Red Hat Query Time
graph_vlabel time
time.label msec
I'm not sure of the value in tracking the above though. The response time can be affected: if the query is an initial lookup, if the answer is cached locally, depending on server load, depending on intervening network congestion, etc.
Note: the above may be a bit buggy as I've written it on the fly, but it should give you a good starting point. That it returned the above output is a good sign.
In any case, recommend reading the following before you write your own: http://munin-monitoring.org/wiki/HowToWritePlugins
Fork is a great tool in unix.We can use it to generate our copy and change its behaviour.But I don't know the history of fork.
Does someone can tell me the story?
Actually, unlike many of the basic UNIX features, fork was a relative latecomer (a).
The earliest existence of multiple processes within UNIX consisted of a few (fixed number of) processes, one per terminal that was attached to the PDP-7 machine (b).
The basic idea was that the shell process for a given terminal would accept a command from the user, locate the program file, load a small bootstrap program into high memory and jump to it, passing enough details for the bootstrap code to load the program file.
The bootstrap code, after loading the program into low memory (overwriting the shell), would then jump to it.
When the program was finished, it would call exit but it wasn't like the exit we know and love today. This exit would simply reload the shell and run it using pretty much the same method used to load the program in the first place.
So it was really more like a rudimentary exec command, the one that replaces your current program with another, in the same process space.
The shell would exec your program then, when your program was done, it would again exec the shell by calling exit.
This method was similar to that found in many other interactive systems at the time, including the Multics from whence UNIX got its name.
From the two-way exec, it was actually not that big a leap to adding fork as a process duplicator to work in conjunction. While many systems run another program directly, it's this "just add what's needed" method which is responsible for the separation of duties between fork and exec in UNIX. It also resulted in a very simple fork function.
If you're interested in the early history of various features(c) of Unix, you cannot go past the article The Evolution of the Unix Time-Sharing System by Dennis Ritchie, presented at a 1979 conference in Australia, and subsequently published by AT&T.
(a) Though I mean latecomer in the sense that the separation of the four fundamental forces in the universe was "late", happening some 0.00000000001 seconds after the big bang.</humour>.
(b) Since a question was raised in a comment as to how the shells were originally started off, there's a great resource holding very early source code for Unix over at The Unix Heritage Society, specifically the source code archives and, in particular, the first edition.
The init.s file from the first edition shows how the fixed number of shell processes were created (slightly reformatted):
...
mov $itab, r1 / address of table to r1
1:
mov (r1)+, r0 / 'x, x=0, 1... to r0
beq 1f / branch if table end
movb r0, ttyx+8 / put symbol in ttyx
jsr pc, dfork / go to make new init for this ttyx
mov r0, (r1)+ / save child id in word offer '0, '1, etc
br 1b / set up next child
1:
...
itab:
'0; ..
'1; ..
'2; ..
'3; ..
'4; ..
'5; ..
'6; ..
'7; ..
0
Here you can see the snippet which creates the processes for each connected terminal. These are the days of hard-coded values, no auto detection of terminal quantity involved. The zero-terminated table at itab is used to create a number of processes and hopefully the comments from the code explain how (the only possibly tricky bit is the labels - though there are multiple 1 labels, you branch to the nearest one in a given direction, hence 1b means the closest 1 label in the backwards direction).
The code shown simply processes the table, calling dfork to create a process for each terminal and start getty, the login prompt. The getty program, in turn, eventually started the shell. From that point, it's as I described in the main part of this answer.
(c) No paths (and use of temporary links to get around this limitation), limited processes, why there's a GECOS field in the password file, and all sorts of other trivia, generally interesting only to uber-geeks, of course.