Problem starting JACK server "Jack Server is not running or cannot be started"

I haven't been able to get JACK to work despite googling and reading on forums. Please help me to get JACK to work. I am attaching the message log of JACK Control here.

02:15:40.109 Patchbay deactivated.
02:15:40.117 Statistics reset.
02:15:40.123 ALSA connection change.
02:15:40.147 D-BUS: Service is available (org.jackaudio.service aka jackdbus).
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
02:15:40.169 ALSA connection graph change.
02:15:43.877 D-BUS: JACK server could not be started. Sorry
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started
Mon Dec  8 02:15:43 2014: Starting jack server...
Mon Dec  8 02:15:43 2014: JACK server starting in realtime mode with priority 10
Mon Dec  8 02:15:43 2014: ERROR: Cannot lock down 82274202 byte memory area (Cannot allocate memory)
Mon Dec  8 02:15:43 2014: ERROR: cannot register object path "/org/freedesktop/ReserveDevice1/Audio0": A handler is already registered for /org/freedesktop/ReserveDevice1/Audio0
Mon Dec  8 02:15:43 2014: ERROR: Failed to acquire device name : Audio0 error : A handler is already registered for /org/freedesktop/ReserveDevice1/Audio0
Mon Dec  8 02:15:43 2014: ERROR: Audio device hw:0 cannot be acquired...
Mon Dec  8 02:15:43 2014: ERROR: Cannot initialize driver
Mon Dec  8 02:15:43 2014: ERROR: JackServer::Open failed with -1
Mon Dec  8 02:15:43 2014: ERROR: Failed to open server
Mon Dec  8 02:15:45 2014: Saving settings to "/home/rythem/.config/jack/conf.xml" ...
02:15:47.373 Could not connect to JACK server as client. - Overall operation failed. - Unable to connect to server. Please check the messages window for more info.
Cannot connect to server socket err = No such file or directory
Cannot connect to server request channel
jack server is not running or cannot be started

First you need to kill the existing pulseaudio process, start the jack_control process and re-start the pulseaudio process.

Please use the below commands:

pulseaudio --kill

jack_control start

jack_control exit

pulseaudio --start

Try using pasuspender with qjackctl. Like this:

pasuspender qjackctl

It should "pause" pulseaudio while qjackctl runs and "respawn" pulseaudio when qjackctl is terminated.

You are trying to run Jack with real-time priorities, and Jack does not configure that by default in Ubuntu. There are two ways to solve this:

1) Don't use realtime priorities.

By CLI you can start Jack without realtime, using jackd -r & - see man jackd for more details.

If you sudo apt install qjackctl to can run the GUI "Qjackctl", and in the 'Setup' section unclick "Realtime"

2) Setup realtime for Jack, as decribed in http://www.jackaudio.org/faq/linux_rt_config.html

Open a terminal and enter

sudo nano /etc/security/limits.d/99-realtime.conf

Add the lines

@realtime   -  rtprio     99
@realtime   -  memlock    unlimited

Press Ctrl+o and then Ctrl+x to save and exit the file.

Create and add yourself to the 'realtime' group:

sudo groupadd realtime
sudo usermod -a -G realtime yourUserID

Logout and back in.