TypeError: Cannot read property 'on' of undefined

[ohardy]

I use onchange package which crash in tree-kill. Stack trace:

<folder>/node_modules/tree-kill/index.js:78
    ps.stdout.on('data', function (data) {
             ^

TypeError: Cannot read property 'on' of undefined
    at buildProcessTree (/***/node_modules/tree-kill/index.js:78:14)
    at /***/node_modules/tree-kill/index.js:99:11
    at Array.forEach (native)
    at ChildProcess.onClose (/***/node_modules/tree-kill/index.js:94:31)
    at emitTwo (events.js:106:13)
    at ChildProcess.emit (events.js:192:7)
    at maybeClose (internal/child_process.js:890:16)
    at Socket.<anonymous> (internal/child_process.js:334:11)
    at emitOne (events.js:96:13)
    at Socket.emit (events.js:189:7)

[billiegoose]

If I understand correctly, you are using the onchange package and it is using tree-kill? I don't yet have enough information to figure out what went wrong. The error Cannot read property 'on' of undefined would imply that ps.stdout is undefined, but I have never seen that happen before. Could you add some more details like what: operating system, Node version?

[ohardy]

I hope it will help you

Node version: 7.5.0

I added some debug and added a test to not call ps.stdout.on if ps.stdout is null and that's it:

onchange: change to src/server.js
onchange: killing command 41413 and restarting
kill(41413, 'SIGTERM');
pgrep -P 41413
pgrep -P 1
pgrep -P 61
pgrep -P 62

toggle full log entire log

``` pgrep -P 64 pgrep -P 65 pgrep -P 66 pgrep -P 68 pgrep -P 70 pgrep -P 72 pgrep -P 73 pgrep -P 74 pgrep -P 75 pgrep -P 81 pgrep -P 85 pgrep -P 87 pgrep -P 88 pgrep -P 96 pgrep -P 99 pgrep -P 103 pgrep -P 104 pgrep -P 107 pgrep -P 109 pgrep -P 111 pgrep -P 112 pgrep -P 113 pgrep -P 114 pgrep -P 115 pgrep -P 116 pgrep -P 118 pgrep -P 120 pgrep -P 121 pgrep -P 122 pgrep -P 123 pgrep -P 127 pgrep -P 128 pgrep -P 129 pgrep -P 130 pgrep -P 132 pgrep -P 133 pgrep -P 134 pgrep -P 135 pgrep -P 142 pgrep -P 150 pgrep -P 163 pgrep -P 167 pgrep -P 173 pgrep -P 184 pgrep -P 186 pgrep -P 202 pgrep -P 233 pgrep -P 235 pgrep -P 236 pgrep -P 237 pgrep -P 238 pgrep -P 249 pgrep -P 250 pgrep -P 253 pgrep -P 254 pgrep -P 255 pgrep -P 256 pgrep -P 265 pgrep -P 270 pgrep -P 273 pgrep -P 274 pgrep -P 275 pgrep -P 287 pgrep -P 288 pgrep -P 291 pgrep -P 307 pgrep -P 319 pgrep -P 336 pgrep -P 347 pgrep -P 354 pgrep -P 355 pgrep -P 357 pgrep -P 359 pgrep -P 360 pgrep -P 361 pgrep -P 362 pgrep -P 363 pgrep -P 368 pgrep -P 370 pgrep -P 371 pgrep -P 373 pgrep -P 374 pgrep -P 376 pgrep -P 379 pgrep -P 380 pgrep -P 381 pgrep -P 382 pgrep -P 384 pgrep -P 385 pgrep -P 386 pgrep -P 388 pgrep -P 391 pgrep -P 395 pgrep -P 397 pgrep -P 398 pgrep -P 407 pgrep -P 409 pgrep -P 410 pgrep -P 412 pgrep -P 414 pgrep -P 419 pgrep -P 420 pgrep -P 421 pgrep -P 422 pgrep -P 426 pgrep -P 428 pgrep -P 429 pgrep -P 433 pgrep -P 434 pgrep -P 435 pgrep -P 438 pgrep -P 439 pgrep -P 440 pgrep -P 442 pgrep -P 446 pgrep -P 451 pgrep -P 453 pgrep -P 467 pgrep -P 470 pgrep -P 492 pgrep -P 493 pgrep -P 495 pgrep -P 503 pgrep -P 590 pgrep -P 593 pgrep -P 617 pgrep -P 671 pgrep -P 677 pgrep -P 678 pgrep -P 683 pgrep -P 685 pgrep -P 687 pgrep -P 691 pgrep -P 692 pgrep -P 693 pgrep -P 695 pgrep -P 696 pgrep -P 703 pgrep -P 704 pgrep -P 705 pgrep -P 707 pgrep -P 709 pgrep -P 710 pgrep -P 712 pgrep -P 731 pgrep -P 735 pgrep -P 762 pgrep -P 778 pgrep -P 787 pgrep -P 788 pgrep -P 790 pgrep -P 797 pgrep -P 802 pgrep -P 829 pgrep -P 832 pgrep -P 833 pgrep -P 835 pgrep -P 841 pgrep -P 842 pgrep -P 843 pgrep -P 847 pgrep -P 859 pgrep -P 1014 pgrep -P 1016 pgrep -P 1017 pgrep -P 1026 pgrep -P 1030 pgrep -P 1048 pgrep -P 1049 pgrep -P 1051 pgrep -P 1054 pgrep -P 1061 pgrep -P 1062 pgrep -P 1063 pgrep -P 1067 pgrep -P 1068 pgrep -P 1069 pgrep -P 1070 pgrep -P 1071 pgrep -P 1072 pgrep -P 1073 pgrep -P 1075 pgrep -P 1086 pgrep -P 1094 pgrep -P 1332 pgrep -P 1484 pgrep -P 3613 pgrep -P 5566 pgrep -P 5602 pgrep -P 5687 pgrep -P 5714 pgrep -P 5736 pgrep -P 5786 pgrep -P 11385 pgrep -P 11698 pgrep -P 13169 pgrep -P 20376 pgrep -P 24392 pgrep -P 24480 pgrep -P 28842 pgrep -P 29151 pgrep -P 29152 pgrep -P 29153 pgrep -P 34919 pgrep -P 35813 pgrep -P 35893 pgrep -P 35894 pgrep -P 36709 pgrep -P 37880 pgrep -P 37990 pgrep -P 37997 pgrep -P 38177 pgrep -P 38178 pgrep -P 38919 pgrep -P 38921 pgrep -P 38925 pgrep -P 38975 pgrep -P 38976 pgrep -P 38982 pgrep -P 38983 pgrep -P 38985 pgrep -P 38986 pgrep -P 38988 pgrep -P 38989 pgrep -P 38997 pgrep -P 39008 pgrep -P 39013 pgrep -P 39014 pgrep -P 39019 pgrep -P 39069 pgrep -P 39070 pgrep -P 39482 pgrep -P 39483 pgrep -P 39659 pgrep -P 40085 pgrep -P 40086 pgrep -P 40087 pgrep -P 40088 pgrep -P 40089 pgrep -P 40090 pgrep -P 40091 pgrep -P 40443 pgrep -P 40513 pgrep -P 40514 pgrep -P 40515 pgrep -P 40518 pgrep -P 40521 pgrep -P 40522 pgrep -P 40525 pgrep -P 40526 pgrep -P 40537 pgrep -P 40637 pgrep -P 40746 pgrep -P 40960 pgrep -P 40961 pgrep -P 40962 pgrep -P 40963 pgrep -P 40964 pgrep -P 40965 pgrep -P 40983 pgrep -P 40989 pgrep -P 40990 pgrep -P 41023 pgrep -P 41104 pgrep -P 41132 pgrep -P 42175 pgrep -P 42262 pgrep -P 42263 pgrep -P 42266 pgrep -P 42267 pgrep -P 42268 pgrep -P 42418 pgrep -P 42519 pgrep -P 42520 pgrep -P 42524 pgrep -P 42543 pgrep -P 42551 pgrep -P 42647 pgrep -P 45698 pgrep -P 51820 pgrep -P 51825 pgrep -P 51854 pgrep -P 53170 pgrep -P 64193 pgrep -P 64195 pgrep -P 64208 pgrep -P 64218 pgrep -P 64347 pgrep -P 64988 pgrep -P 65139 pgrep -P 65176 pgrep -P 65231 pgrep -P 65382 pgrep -P 65383 pgrep -P 65384 pgrep -P 70158 pgrep -P 70159 pgrep -P 72167 pgrep -P 72174 pgrep -P 75442 pgrep -P 75447 pgrep -P 75577 pgrep -P 75586 pgrep -P 75588 pgrep -P 80995 pgrep -P 81249 pgrep -P 84796 pgrep -P 20887 pgrep -P 24009 pgrep -P 24024 pgrep -P 24026 pgrep -P 24634 pgrep -P 24645 pgrep -P 24665 pgrep -P 24666 pgrep -P 24668 pgrep -P 24760 pgrep -P 24774 pgrep -P 27036 pgrep -P 27047 pgrep -P 27048 pgrep -P 27049 pgrep -P 27050 pgrep -P 27051 pgrep -P 27052 pgrep -P 27053 pgrep -P 27054 pgrep -P 27055 pgrep -P 27056 pgrep -P 27057 pgrep -P 27061 pgrep -P 52882 pgrep -P 52884 pgrep -P 52898 pgrep -P 64385 pgrep -P 64516 pgrep -P 68527 pgrep -P 68575 pgrep -P 68576 pgrep -P 68577 pgrep -P 68578 pgrep -P 69022 pgrep -P 69500 pgrep -P 69504 pgrep -P 69598 pgrep -P 69628 pgrep -P 69665 pgrep -P 69743 pgrep -P 69903 pgrep -P 69939 pgrep -P 70018 pgrep -P 70074 pgrep -P 70119 pgrep -P 70181 pgrep -P 70268 pgrep -P 70292 pgrep -P 70296 pgrep -P 70309 pgrep -P 70336 pgrep -P 70337 pgrep -P 70351 pgrep -P 70352 pgrep -P 70609 pgrep -P 70614 pgrep -P 70617 pgrep -P 57986 pgrep -P 29079 pgrep -P 29169 pgrep -P 29170 pgrep -P 29181 pgrep -P 29183 pgrep -P 29185 pgrep -P 29186 pgrep -P 29187 pgrep -P 29188 pgrep -P 29237 pgrep -P 29250 pgrep -P 29253 pgrep -P 29594 pgrep -P 80275 pgrep -P 80352 pgrep -P 80357 pgrep -P 14550 pgrep -P 23608 pgrep -P 25083 pgrep -P 28381 pgrep -P 28382 pgrep -P 28383 pgrep -P 28384 pgrep -P 28385 pgrep -P 28386 pgrep -P 28387 pgrep -P 28388 pgrep -P 28389 pgrep -P 28390 pgrep -P 29216 pgrep -P 33166 pgrep -P 33214 pgrep -P 33708 pgrep -P 33713 pgrep -P 33716 pgrep -P 33743 pgrep -P 33744 pgrep -P 33745 pgrep -P 33746 pgrep -P 33747 pgrep -P 33748 pgrep -P 33749 pgrep -P 33750 pgrep -P 33751 pgrep -P 33752 pgrep -P 34658 ```

pgrep -P 34661
pgrep -P 34668
pgrep -P 35612
Null stdout for : spawnChildProcessesList(35612)
pgrep -P 35636
Null stdout for : spawnChildProcessesList(35636)
pgrep -P 35641
Null stdout for : spawnChildProcessesList(35641)
pgrep -P 35669
Null stdout for : spawnChildProcessesList(35669)
pgrep -P 35714
Null stdout for : spawnChildProcessesList(35714)
pgrep -P 36565
Null stdout for : spawnChildProcessesList(36565)
pgrep -P 36566
Null stdout for : spawnChildProcessesList(36566)
pgrep -P 36567
Null stdout for : spawnChildProcessesList(36567)
pgrep -P 36731
Null stdout for : spawnChildProcessesList(36731)
pgrep -P 36732
Null stdout for : spawnChildProcessesList(36732)
pgrep -P 36733
Null stdout for : spawnChildProcessesList(36733)
pgrep -P 36734
Null stdout for : spawnChildProcessesList(36734)
pgrep -P 36738
Null stdout for : spawnChildProcessesList(36738)
pgrep -P 36739
Null stdout for : spawnChildProcessesList(36739)
pgrep -P 36740
Null stdout for : spawnChildProcessesList(36740)
pgrep -P 36741
Null stdout for : spawnChildProcessesList(36741)
pgrep -P 37001
Null stdout for : spawnChildProcessesList(37001)
pgrep -P 37002
Null stdout for : spawnChildProcessesList(37002)
pgrep -P 37004
Null stdout for : spawnChildProcessesList(37004)
pgrep -P 37006
Null stdout for : spawnChildProcessesList(37006)
pgrep -P 37026
Null stdout for : spawnChildProcessesList(37026)
pgrep -P 40026
Null stdout for : spawnChildProcessesList(40026)
pgrep -P 41303
Null stdout for : spawnChildProcessesList(41303)
pgrep -P 41412
Null stdout for : spawnChildProcessesList(41412)
pgrep -P 41413
Null stdout for : spawnChildProcessesList(41413)
pgrep -P 41424
Null stdout for : spawnChildProcessesList(41424)
events.js:161
      throw er; // Unhandled 'error' event
      ^

Error: spawn pgrep EAGAIN
    at exports._errnoException (util.js:1023:11)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:193:32)
    at onErrorNT (internal/child_process.js:359:16)
    at _combinedTickCallback (internal/process/next_tick.js:74:11)
    at process._tickCallback (internal/process/next_tick.js:98:9)

killAll(tree, signal, callback);

is never called

[Marak]

What happens if you switch back to Node version 6?

[ohardy]

Same bug with v6.9.5

[billiegoose]

Huh. This is on Linux?

[ohardy]

Mac OS 10.12.3

[ohardy]

So i try to fix the issue. I thinks it's a too many process problem for the buildProcessTree part, if i add a setTimeout for each spawn call, no more stdout null bug.

But the other problem is :

kill :  75531 SIGTERM
onClose pid : 75531 code: 0
Object.keys(pidsToProcess).length :  0

So in onClose, i change:

if (code != 0) {

to:

if (code == 0) {

And everything works.

Why do you check the return code of the process ?

[ickma]

I met the same issue as u @ohardy , your solution saved me!

[billiegoose]

Why do you check the return code of the process ?

The return code of pgrep -P tells us whether the process has children that also need to be killed. From the manpage:

EXIT STATUS
       0      One or more processes matched the criteria.
       1      No processes matched.
       2      Syntax error in the command line.
       3      Fatal error: out of memory etc.

By changing the != to == you're bailing out of the recursion prematurely. However the more I study this code, the more I'm not sure it is right. I think the forEach loop and the callback cb invocation creates a race condition. I think this code should probably be refactored to make the control flow simpler, but I don't have the time right now. Long story short @ohardy and @ickma, somehow the process you're trying to kill creates so many children that tree-kill runs into a race condition. The fix suggested will probably keep tree-kill from crashing and never calling killAll, but it might allow children/grandchildren of the process to escape it's killer grasp and become zombies.

If anyone thinks of a better way to do the recursive process killing I'm all ears. I don't have spare cycles to investigate. (And don't have a Mac.) @ickma is yours Mac OSX too?

[DPiaz]

In my case, i removed the option {stdio: 'inherit'} from the call spawn(command, args, options) and works.

[mogutan88]

In my case, I have proctools installed on my macOS at, /usr/local/bin. I confirmed that the output of '/usr/local/bin/pgrep -P' and that of '/usr/bin/pgrep -P' are different. So, uninstalling the proctools, changing the PATH, or even changing the tree-kill/index.js code like below, solved the problem.

    case 'darwin':
        buildProcessTree(pid, tree, pidsToProcess, function (parentPid) {
          return spawn('/usr/bin/pgrep', ['-P', parentPid]);