The error is a segmentation fault, looking at strace and ltrace we see the permission and array check error:

strace:

open("5401/io", O_RDONLY) = 4 read(4, 0x7ffd4c67c360, 4095) = -1 EACCES (Permission denied) close(4) = 0 --- SIGSEGV {si_signo=SIGSEGV, si_code=SEGV_MAPERR, si_addr=0x2} --- +++ killed by SIGSEGV +++ Segmentation fault

ltrace:

[pid 25433] open("5401/io", 0, 07332762347) = 4 [pid 25433] read(4 <no return ...> error: maximum array length seems negative , "5401/io", 4095) = -1 [pid 25433] close(4) = 0 [pid 25433] strchr("5401/io", ':') = nil [pid 25433] strchr("\002\003\004\005\006\a\b\t\n\v\f\r\016\017\020\021\022\023\024\025\026\027\030\031\032\033\034\035\036\037 !"..., '\n' <no return ...> [pid 25433] --- SIGSEGV (Segmentation fault) --- [pid 25433] +++ killed by SIGSEGV +++

Looks like /proc/*/io is not always readable. Will have to handle that properly...

Commit f6232a94 shows that -1 EACCES (Permission denied) should be handled:

	sprintf(buffer, "%d/io", proc->pid);
	fd = open(buffer, O_RDONLY);
	if (fd == -1)
	{
		/*
		 * CONFIG_TASK_IO_ACCOUNTING is not enabled in the Linux kernel or
		 * this version of Linux may not support collecting i/o statistics per
		 * pid.  Report 0's.
		 */
		proc->rchar = 0;
		proc->wchar = 0;
		proc->syscr = 0;
		proc->syscw = 0;
		proc->read_bytes = 0;
		proc->write_bytes = 0;
		proc->cancelled_write_bytes = 0;
		return;
	}
	len = read(fd, buffer, sizeof(buffer) - 1);
	close(fd);

I can't reproduce the segfaulting running lxc/lxd on Gentoo when I run pg_top as a user that does not have read access to io. I'm not sure which close() it would be segfaulting at. Is it still reproducible on the code tagged at 4.0.0-alpha1?

I'm seeing this when running pg_top from the official docker image, and I install pgtop package using apt-get (3.7.0-18-gbbf1f12-3.pgdg90+1). I tried building 4.0+ from source but failed miserably 😢 . Here's what I did:

/# wget https://pg_top.gitlab.io/source/pg_top-4.0.0-alpha2.tar.xz
/# tar xf pg_top-4.0.0-alpha2.tar.xz
/# cd pg_top-4.0.0-alpha2
/pg_top-4.0.0-alpha2# apt install build-essential cmake libpq-dev libbsd-dev
/pg_top-4.0.0-alpha2# cmake CMakeLists.txt
-- machine - linux
-- arch - x86_64
-- pg_config --includedir - /usr/include/postgresql
-- pg_config --libdir - /usr/lib/x86_64-linux-gnu
-- Configuring done
-- Generating done
-- Build files have been written to: /pg_top-4.0.0-alpha2
/pg_top-4.0.0-alpha2# make install
Scanning dependencies of target pg_top
[  7%] Building C object CMakeFiles/pg_top.dir/commands.c.o
[ 14%] Linking C executable pg_top
CMakeFiles/pg_top.dir/display.c.o: In function `display_move':
display.c:(.text+0x2b5): undefined reference to `tgoto'
display.c:(.text+0x2cf): undefined reference to `tputs'
CMakeFiles/pg_top.dir/display.c.o: In function `display_write':
display.c:(.text+0x594): undefined reference to `tgoto'
display.c:(.text+0x5ae): undefined reference to `tputs'
CMakeFiles/pg_top.dir/display.c.o: In function `display_cte':
display.c:(.text+0x7cd): undefined reference to `tputs'
CMakeFiles/pg_top.dir/display.c.o: In function `u_endscreen':
display.c:(.text+0x1ecf): undefined reference to `tgoto'
display.c:(.text+0x1ee9): undefined reference to `tputs'
CMakeFiles/pg_top.dir/screen.c.o: In function `get_screensize':
screen.c:(.text+0x9d): undefined reference to `tgoto'
CMakeFiles/pg_top.dir/screen.c.o: In function `init_termcap':
screen.c:(.text+0x143): undefined reference to `tgetent'
screen.c:(.text+0x1b4): undefined reference to `tgetflag'
screen.c:(.text+0x1d0): undefined reference to `tgetnum'
screen.c:(.text+0x202): undefined reference to `tgetnum'
screen.c:(.text+0x23a): undefined reference to `tgetflag'
screen.c:(.text+0x268): undefined reference to `tgetstr'
screen.c:(.text+0x282): undefined reference to `tgetstr'
screen.c:(.text+0x2a8): undefined reference to `tgetstr'
screen.c:(.text+0x2da): undefined reference to `tgetstr'
screen.c:(.text+0x2f4): undefined reference to `tgetstr'
CMakeFiles/pg_top.dir/screen.c.o:screen.c:(.text+0x30e): more undefined references to `tgetstr' follow
CMakeFiles/pg_top.dir/screen.c.o: In function `init_termcap':
screen.c:(.text+0x394): undefined reference to `tgoto'
CMakeFiles/pg_top.dir/screen.c.o: In function `init_screen':
screen.c:(.text+0x4e1): undefined reference to `tputs'
CMakeFiles/pg_top.dir/screen.c.o: In function `end_screen':
screen.c:(.text+0x51d): undefined reference to `tputs'
screen.c:(.text+0x544): undefined reference to `tputs'
screen.c:(.text+0x57a): undefined reference to `tputs'
CMakeFiles/pg_top.dir/screen.c.o: In function `reinit_screen':
screen.c:(.text+0x5ff): undefined reference to `tputs'
CMakeFiles/pg_top.dir/screen.c.o:screen.c:(.text+0x640): more undefined references to `tputs' follow
collect2: error: ld returned 1 exit status
CMakeFiles/pg_top.dir/build.make:410: recipe for target 'pg_top' failed
make[2]: *** [pg_top] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/pg_top.dir/all' failed
make[1]: *** [CMakeFiles/pg_top.dir/all] Error 2
Makefile:149: recipe for target 'all' failed
make: *** [all] Error 2

I'm obviously doing something wrong ... can this even compile as-is for debian, or does it need a patch? Is there a chance 4.0 alpha can hit next debian release?

Yes, pg_top should be able to compile as-in on debian.

tputs is provided by curses. libncurses5-dev should take are of that one.

I'm not directly involved in any distro packaging. I'm afraid I'm not sure when packaging will be updated...