liveuser@localhost:~$ gdb -p 11728
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/home/liveuser/.gdbinit:19: Error in sourced command file:
No symbol table is loaded.  Use the "file" command.
Attaching to process 11728
Reading symbols from /usr/bin/emacsclient...Reading symbols from /usr/lib/debug/usr/bin/emacsclient.debug...done.
done.
Reading symbols from /lib64/libc.so.6...Reading symbols from /usr/lib/debug/usr/lib64/libc-2.22.so.debug...done.
done.
Reading symbols from /lib64/ld-linux-x86-64.so.2...Reading symbols from /usr/lib/debug/usr/lib64/ld-2.22.so.debug...done.
done.
Reading symbols from /lib64/libnss_files.so.2...Reading symbols from /usr/lib/debug/usr/lib64/libnss_files-2.22.so.debug...done.
done.

Program received signal SIGTTIN, Stopped (tty input).
0x00007eff2d8f8dd7 in kill () at ../sysdeps/unix/syscall-template.S:84
84	T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
(gdb) 
(gdb) thread apply all bt full

Thread 1 (process 11728):
#0  0x00007eff2d8f8dd7 in kill () at ../sysdeps/unix/syscall-template.S:84
No locals.
#1  0x0000000000402a9e in handle_sigcont (signalnum=18)
    at ../../lib-src/emacsclient.c:1112
        old_errno = 0
        pgrp = 11728
        tcpgrp = <optimized out>
#2  <signal handler called>
No locals.
#3  0x00007eff2d8f8da0 in __sigprocmask (how=how@entry=2, 
    set=set@entry=0x7fffcdf335c0, oset=oset@entry=0x0)
    at ../sysdeps/unix/sysv/linux/x86_64/sigprocmask.c:39
        resultvar = 0
#4  0x00000000004029f8 in handle_sigtstp (signalnum=20)
    at ../../lib-src/emacsclient.c:1140
        old_errno = 0
        set = {__val = {0, 140736648656468, 139634449943984, 140736648657280, 
            139634443759616, 139634443756832, 0, 140736648656472, 521243869, 
            8144435, 15466360082538692637, 140736648656688, 140736648656468, 
            140736648656672, 28333888, 15466360082538692608}}
#5  <signal handler called>
---Type <return> to continue, or q <return> to quit---
No locals.
#6  0x00007eff2d9c7a2b in __libc_recv (fd=4, buf=buf@entry=0x7fffcdf33c90, 
    n=n@entry=8192, flags=765229613, flags@entry=0)
    at ../sysdeps/unix/sysv/linux/x86_64/recv.c:28
        __arg6 = 0
        __arg3 = 8192
        _a5 = 0
        _a2 = 140736648658064
        __arg4 = 0
        __arg1 = 4
        _a6 = 0
        _a3 = 8192
        resultvar = <optimized out>
        __arg5 = 0
        __arg2 = 140736648658064
        _a4 = 0
        _a1 = 4
        resultvar = <optimized out>
        sc_ret = <optimized out>
#7  0x0000000000401ce0 in recv (__flags=0, __n=8192, __buf=0x7fffcdf33c90, 
    __fd=<optimized out>) at /usr/include/bits/socket2.h:44
No locals.
#8  main (argc=3, argv=0x7fffcdf35db8) at ../../lib-src/emacsclient.c:1806
---Type <return> to continue, or q <return> to quit---
        p = <optimized out>
        end_p = <optimized out>
        rl = <optimized out>
        needlf = 0
        cwd = <optimized out>
        str = <optimized out>
        string = "-emacs-pid 1132", '\000' <repeats 5449 times>...
        start_daemon_if_needed = <optimized out>
        exit_status = <optimized out>
(gdb)