QProcess: run app via sudo

debian

Hello!
I should execute several command which require privileged access from my app which run as non-privileged.
For this I was add command to /etc/sudoerc and allow run it without password, command work if I run it at shell

~ $ sudo ping -c 3 ya.ru
PING ya.ru (87.250.250.242): 56 data bytes
64 bytes from 87.250.250.242: seq=0 ttl=249 time=9.118 ms
64 bytes from 87.250.250.242: seq=1 ttl=249 time=8.910 ms
64 bytes from 87.250.250.242: seq=2 ttl=249 time=8.949 ms

--- ya.ru ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 8.910/8.992/9.118 ms

Now I add QProcess to my app

QProcess pingProcess;
pingProcess.start("/usr/bin/sudo",{"/bin/ping -c 5 ya.ru"});

Unfortunately this is not work, after run app I see Password: at console output, at app finish console output contain follow lines

...............
QProcess: Destroyed while process ("/usr/bin/sudo") is still running.
error ping "sudo: unable to mkdir /run: Read-only file system\nsudo: a password is required\n"
................

and sudo log contain line command not allowed, look like what sudo can't found or can't read /etc/sudoerc.
How should I correct use QProcess for run externals app via sudo ?
Thank you.

KroMignon

@debian said in QProcess: run app via sudo:

QProcess pingProcess;
pingProcess.start("/usr/bin/sudo",{"/bin/ping -c 5 ya.ru"});

This is the wrong way to do, each parameter should be an entry in the QStringList.
This should work:

QProcess pingProcess;
pingProcess.start("/usr/bin/sudo", QStringList() << "/bin/ping" << "-c" << "5" << "ya.ru")

debian

@KroMignon , thank you!
Can you provide more details?

KroMignon

@debian said in QProcess: run app via sudo:

Can you provide more details?

More than what is documentation?
https://doc.qt.io/qt-5/qprocess.html#details

KroMignon

@debian said in QProcess: run app via sudo:

Can you provide more details?

One more think to note, as QProcess instance is on stack, you should use QProcess::execute() to wait until process is done:

QProcess::execute("/usr/bin/sudo", QStringList() << "/bin/ping" << "-c" << "5" << "ya.ru")

or do it yourself with waitForFinished(), so you could add a timeout:

QProcess pingProcess;
pingProcess.start("/usr/bin/sudo", QStringList() << "/bin/ping" << "-c" << "5" << "ya.ru")
if(!pingProcess.waitForStarted(1000))
   qDebug() << "Could NOT start sudo!!";
else if(!pingProcess.waitForFinished(20000))
   qDebug() << "Ping is not ending!!!";
else
  qDebug() << "Done.";

JonB

@debian
For my own interest, why do you need sudo/"privileged access" to run ping -c 5 ya.ru?

debian

@JonB , this is embedded system, I'm use busybox, so ping is not separate app and I can't use linux capabilities, this is simplink to busybox.

JonB

@debian OK, thanks for replying, embedded systems/"busybox"/"simplink" are quite beyond me! Under plain Linux you would not need sudo for ping.

debian

$ /usr/sbin/getcap /bin/ping
/bin/ping cap_net_raw=ep

This work because /bin/ping have capabilites
https://man7.org/linux/man-pages/man7/capabilities.7.html

CAP_NET_RAW

Use RAW and PACKET sockets;

bind to any address for transparent proxying.