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]);