I want some way to know if the Capslock is active or not, thought I can use xet for this purpose, using pipe, by popen('xset -q | grep Capslock') I am able to find out, but I want some way by which there is no use of the commands, in the C program, is there any way to know this.
One more thing I want to ask in this context, xset doens't work in the console mode in linux, I do alt+ctrl+f1 then login there and if try to run xset -q this will throw error, perhaps this can't communicate with the XWindows in console, so what solution can be for this case.
I want some way to know if the Capslock is active or not
You probably want XkbGetIndicatorState. For instance:
#include <stdio.h>
#include <stdlib.h>
#include <X11/XKBlib.h>
/* Compile this with -lX11 */
int main ()
{
Display *display;
Status status;
unsigned state;
display = XOpenDisplay (getenv ("DISPLAY"));
if (!display)
return 1;
if (XkbGetIndicatorState (display, XkbUseCoreKbd, &state) != Success)
return 2;
printf ("Caps Lock is %s\n", (state & 1) ? "on" : "off");
return 0;
}
Alternatively, you can go with the same approach that is used in xset and use XkbGetNamedIndicator which is a more general function.
Download the source to xset and see how it does things. It's not black magic. It will give you the functions to call to get/set the things you want. For xset to work, it must be invoked under the Window manager, so it can't be done from a VT console.
For the VT, from man 2 ioctl_console, you can use the KDGKBLED and KDSKBLED ioctls to get/set the flags.
Related
For unit testing purposes, I want to be able to run a bare-metal binary with qemu and capture it's output.
Sample file:
#include <stdio.h>
#include <stdint.h>
static void qemu_exit() {
register uint32_t r0 __asm__("r0");
r0 = 0x18;
register uint32_t r1 __asm__("r1");
r1 = 0x20026;
__asm__ volatile("bkpt #0xAB");
}
int main(void) {
puts("This is some example text that I want to capture");
qemu_exit();
return 0;
}
Running with:
qemu-system-gnuarmeclipse --nographic --no-reboot \
--board STM32F4-Discovery --mcu STM32F429ZI \
--semihosting-config enable=on,target=native \
--image <binary>
Displayed to the console is:
QEMU 2.8.0-13 monitor - type 'help' for more information
(qemu) This is some example text that I want to capture
This 'example text' is generated within QEMU and so redirecting stdout to a file does not capture it (only: QEMU 2.8.0-13 monitor - type 'help' for more information
(qemu)). Looking at the available qemu logging options -d help does not offer anything as far as I can see.
EDIT
A hacky solution is to use script to capture terminal session:
script --quiet --command <qemu-shell-script-wrapper>
That's not an upstream QEMU, and 2.8 is also quite old, but hopefully the same things that work with upstream QEMU will work there.
Firstly, assuming you're not actually using the monitor, you can get rid of that part of the output by dropping '--nographic' and instead using '-display none'. (--nographic does a lot of things all at once, including both "no graphical display" and also "default serial output to the terminal, add a QEMU monitor and multiplex the monitor and the serial", among other things. It's convenient if that's what you want but sometimes it's less confusing to specify everything separately.)
Secondly, you say you're using semihosting output but is the guest's stdlib definitely using semihosting for its puts() string output and not serial port (UART) output? The output will come out on the terminal either way but how you tell QEMU to redirect it somewhere else will differ. (I suspect it may be using UART output, because if it were using semihosting output then the redirection of stdout that you tried should have worked.)
If the output from the guest is via the serial port then you can control where it goes using the '-serial' option (most simply, "-serial stdio" to send to stdout, but you can also do more complicated things like sending to files, pipes or TCP sockets.). If it's via semihosting then you can control where it goes using the 'chardev=id' suboption of -semihosting-config.
Hi I am new to the linux environment. I am trying to create daemon process.
#include<stdio.h>
int main()
{
int a=10,b=10,c;
c=sum(a,b);
printf("%d",c);
return (0);
}
int sum(int a,int b)
{
return a+b;
}
I want to create daemon process of it. May i know how can do this? Any help would be appreciated. Thank you.
A daemon generally doesn't use its standard input and output streams, so it is unclear how your program could be run as a daemon. And a daemon program usually don't have any terminal, so it cannot use clrscr. Read also the tty demystified page, and also daemon(7).
I recommend reading some good introduction to Linux programming, like the old freely downloadable ALP (or something newer). We can't explain all of it here, and you need to read an entire book. See also intro(2) and syscalls(2).
I also recommend reading more about OSes, e.g. the freely available Operating Systems: Three Easy Pieces textbook.
You could use the daemon(3) function in your C program to run it as a daemon (but then, you are likely to not have any input and output). You may want to log messages using syslog(3).
You might consider job control facilities of your shell. You could run your program in the background (e.g. type myprog myarg & in your interactive shell). You could use the batch command. However neither background processes nor batch jobs are technically daemons.
Perhaps you want to code some ONC-RPC or JSONRPC or Web API server and client. You'll find libraries for that. See also pipe(7), socket(7)
(take several days or several weeks to read much more)
First find what are the properties of daemon process, as of my knowledge a daemon process have these properties:
Should not have any parent (it itself should be parent)
Process itself is a session leader.
Environment change to root.
File mode creating mask should be zero.
No controlling terminal.
All terminal should be removed
Should not be un-mounted .
Implement the code by considering above properties which is
int i=0;
int main()
{
int pid;
pid=fork();
if(pid!=0) {
/** you can add your task here , whatever you want to run in background **/
exit(0);
}
else
{
setsid();//setting sessions
chdir("/");//root.. should'nt beunmounted
umask(0);
close(0);//all terminal are removed
close(1);
close(2);
while(1)
{
printf("i = %d \n",i);
i++;
}
}
return 0;
}
or you can go through man page of daemon()
int daemon(int nochdir, int noclose);
I hope it helps.
Instead of writing the code to make the C program a daemon I would go with an already mature tool like supervisor:
http://supervisord.org/
I think this below will work
screen cmd arg1 arg2
You can also try
nohup cmd arg1
I have little issue with XOpenDisplay function. In school I can run program and it works good when using XOpenDisplay("ip:0"), but on my local machine in home when I run program (changed ip on current) got "Segmentation fault (core dumped)", but with empy string XOpenDisplay("") it works fine. I need to be able to use ip. Used host +, but nothing changes.
My system is Kubuntu 14.04.1: 3.16.0-30-generic #40~14.04.1-Ubuntu SMP Thu Jan 15 17:43:14 UTC 2015
Here is code of program:
#include <X11/Xlib.h>
#include <X11/X.h>
#include <stdio.h>
Display *mydisplay;
Window mywindow;
XSetWindowAttributes mywindowattributes;
XGCValues mygcvalues;
GC mygc;
Visual *myvisual;
int mydepth;
int myscreen;
Colormap mycolormap;
XColor mycolor,mycolor1,dummy;
int i;
main()
{
mydisplay = XOpenDisplay("192.168.0.12:0");
myscreen = DefaultScreen(mydisplay);
myvisual = DefaultVisual(mydisplay,myscreen);
mydepth = DefaultDepth(mydisplay,myscreen);
mywindowattributes.background_pixel = XWhitePixel(mydisplay,myscreen);
mywindowattributes.override_redirect = True;
mywindow = XCreateWindow(mydisplay,XRootWindow(mydisplay,myscreen),
0,0,500,500,10,mydepth,InputOutput,
myvisual,CWBackPixel|CWOverrideRedirect,
&mywindowattributes);
mycolormap = DefaultColormap(mydisplay,myscreen);
XAllocNamedColor(mydisplay,mycolormap,"cyan",&mycolor,&dummy);
XAllocNamedColor(mydisplay,mycolormap,"red",&mycolor1,&dummy);
XMapWindow(mydisplay,mywindow);
mygc = DefaultGC(mydisplay,myscreen);
XSetForeground(mydisplay,mygc,mycolor.pixel);
XFillRectangle(mydisplay,mywindow,mygc,100,100,300,300);
XSetForeground(mydisplay,mygc,mycolor1.pixel);
XSetFunction(mydisplay,mygc,GXcopy);
XSetLineAttributes(mydisplay,mygc,10,LineSolid,CapProjecting,JoinMiter);
XDrawLine(mydisplay,mywindow,mygc,100,100,400,400);
XDrawLine(mydisplay,mywindow,mygc,100,400,400,100);
XFlush(mydisplay);
sleep(10);
XCloseDisplay(mydisplay);
exit(0);
}
I can only guess that need to set something, but have no idea where is that option.
You shall always check whether functions returned successfully, or not. It is not a Haskell, where all the checking done for you by monad, it is C. As for your particular case, the problem is that the function XOpenDisplay fails and returns null for you. In the next line you're trying to use DefaultScreen with the result. The DefaultScreen is defined as
#define DefaultScreen(dpy) ((dpy)->default_screen)
I.e. it just a macro, which using the first argument as a pointer. In your case it does ((0)->default_screen), i.e. it dereferencing the null pointer, and that leads to the segfault you see.
Also, about the XOpenDisplay("192.168.0.12:0"); — you didn't mentioned that you're trying to connect to another PC, so, if it's the same computer where the app running, try to call the function as XOpenDisplay("127.0.0.1:0");
UPD: okay, I tried to run the code at my PC, and the function doesn't work for me too. To find the reason I started the code under strace app, and saw
…
connect(3, {sa_family=AF_INET, sin_port=htons(6000), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 ECONNREFUSED (Connection refused)
…
Aha! So, the app trying to connect to XServer, but Xserver refuses the connection. Actually, it have a security reason to disable it by default — so, that nobody would connect to your XServer from a network unless you specifically allowed it. For the function to work you need to launch your XServer with the option that allows such a connection. Right now DisplayManagers are the ones, who manages xsessions, so you need to set some option depending on your DM.
The solution for lightdm
Open the /etc/lightdm/lightdm.conf, and paste the line xserver-allow-tcp=true in the section [SeatDefaults](you will see it).
The solution for gdm
Edit the file /etc/gdm/gdm.schemas, you will find there something like
<schema>
<key>security/DisallowTCP</key>
<signature>b</signature>
<default>true</default>
</schema>
Change the true to false.
Linux C program:
What function call can check if running in X Window?
If not in X Window, then printf.
Do you mean something like this:
#include <X11/Xlib.h>
// ...
char *display_name = NULL;
/* connect to X server */
if ( (display=XOpenDisplay(display_name)) == NULL )
{
//printf or whatever
}
What do you mean "running in X Window"? Do you mean whether your app is running inside a terminal emulator, like rxvt or xterm instead of a physical console? If so you could use the TERM variable I guess, but it's not reliable (since the user can change it to whatever).
The more important quesion is why is this information important to your application?
I wrote a C program/LaunchDaemon that checks if my MacBook is at home (connected to my WLAN). If so, it disables my password protection; if not, it enables it.
Easy. But the problem is that when I take my MacBook anywhere else and password protection is disabled, it will wake up without a password protection.
My fix for this would be: enable the password protection every time just before it goes to sleep.
QUESTION: is there any way find out when my Mac is preparing for sleep? Some interupt I can let my program listen to?
You can do it using I/O Kit, check Apple's QA1340: Registering and
unregistering for sleep and wake notifications. You may also want to
analyze the SleepWatcher utility sources or use/integrate for your needs.
From the homepage:
SleepWatcher 2.2 (running with Mac OS X 10.5 to 10.8, source code included)
is a command line tool (daemon) for Mac OS X that monitors sleep, wakeup and
idleness of a Mac. It can be used to execute a Unix command when the Mac or
the display of the Mac goes to sleep mode or wakes up, after a given time
without user interaction or when the user resumes activity after a break or
when the power supply of a Mac notebook is attached or detached. It also can
send the Mac to sleep mode or retrieve the time since last user activity. A
little bit knowledge of the Unix command line is required to benefit from
this software.
I attach below the contents of my C file beforesleep.c which executes some command line commands (in my case shell commands and AppleScript scripts) when a "will sleep" notification is received.
Where you can put your code:
In order to run your code when the mac is going to sleep, just replace the system(...) calls with the code you wish to run.
In my case, I use system() as it allows me to run shell commands passed as strings, but if you prefer to run just C code instead, you can just put your C code there.
How to build it
In order to build this file, I run:
gcc -framework IOKit -framework Cocoa beforesleep.c
Remark
If you are going to use this code, make sure it is always running in background. For example, I have a Cron job which makes sure that this code is always running, and it launches it again in case it is accidentally killed for any reason (although it never happened to me so far). If you are experienced enough, you can find smarter ways to ensure this.
Further info
See this link (already suggested by sidyll) for more details about how this works.
Code template
#include <ctype.h>
#include <stdlib.h>
#include <stdio.h>
#include <mach/mach_port.h>
#include <mach/mach_interface.h>
#include <mach/mach_init.h>
#include <IOKit/pwr_mgt/IOPMLib.h>
#include <IOKit/IOMessage.h>
io_connect_t root_port; // a reference to the Root Power Domain IOService
void
MySleepCallBack( void * refCon, io_service_t service, natural_t messageType, void * messageArgument )
{
switch ( messageType )
{
case kIOMessageCanSystemSleep:
IOAllowPowerChange( root_port, (long)messageArgument );
break;
case kIOMessageSystemWillSleep:
system("/Users/andrea/bin/mylogger.sh");
system("osascript /Users/andrea/bin/pause_clockwork.scpt");
IOAllowPowerChange( root_port, (long)messageArgument );
break;
case kIOMessageSystemWillPowerOn:
//System has started the wake up process...
break;
case kIOMessageSystemHasPoweredOn:
//System has finished waking up...
break;
default:
break;
}
}
int main( int argc, char **argv )
{
// notification port allocated by IORegisterForSystemPower
IONotificationPortRef notifyPortRef;
// notifier object, used to deregister later
io_object_t notifierObject;
// this parameter is passed to the callback
void* refCon;
// register to receive system sleep notifications
root_port = IORegisterForSystemPower( refCon, ¬ifyPortRef, MySleepCallBack, ¬ifierObject );
if ( root_port == 0 )
{
printf("IORegisterForSystemPower failed\n");
return 1;
}
// add the notification port to the application runloop
CFRunLoopAddSource( CFRunLoopGetCurrent(),
IONotificationPortGetRunLoopSource(notifyPortRef), kCFRunLoopCommonModes );
/* Start the run loop to receive sleep notifications. Don't call CFRunLoopRun if this code
is running on the main thread of a Cocoa or Carbon application. Cocoa and Carbon
manage the main thread's run loop for you as part of their event handling
mechanisms.
*/
CFRunLoopRun();
//Not reached, CFRunLoopRun doesn't return in this case.
return (0);
}