net-snmp / Bugs / #2658 HOST-RESOURCES-MIB::hrSystemNumUsers.0 returns wrong number of users

Dan Langille - 2015-08-15

FYI, the value returned appears to go up, but never goes back down.

If you would like to refer to this comment somewhere else in this project, copy and paste the following link:

Bill Fenner - 2015-08-17

Hi Dan,

The code that generates the number of users is at https://sourceforge.net/p/net-snmp/code/ci/master/tree/agent/mibgroup/host/hr_system.c#l665 . It has a pretty naive loop around getutent() (or getutxent() if you have utmpx), and checks for USER_PROCESS (if utmp_p has ut_type) and that the PID is running (if utmp_p has ut_pid).

Sadly I don't currently have a good FreeBSD machine to test this on; is getutent() / getutxent() not the right way to count users?

Bill

If you would like to refer to this comment somewhere else in this project, copy and paste the following link:

Dan Langille - 2015-08-17

Hello Bill,

Fancy meeting you here....

I'm reading https://www.freebsd.org/cgi/man.cgi?query=utmpx&sektion=3&manpath=FreeBSD+10.1-RELEASE and comparing the code you linked to with the code I found here: https://svnweb.freebsd.org/base/head/usr.bin/w/w.c?revision=285550&view=markup#l218

Only the if at lines 222-223 seems relevant as to the differences. What do you think?

If you send me an ssh-key, I will give you a login on a FreeBSD box.

If you would like to refer to this comment somewhere else in this project, copy and paste the following link:

Dan Langille - 2015-08-17

I chatted with Ed Schouten about w. He suggested I try this from the command line:

$ getent utmpx active
[1439589750.958402 -- Fri Aug 14 22:02:30 2015] system boot
[1439844386.475877 -- Mon Aug 17 20:46:26 2015] user process: id="7074732f30000000" pid="80395" user="dan" line="pts/0" host="dent.int.unixathome.org"
[1439645436.408339 -- Sat Aug 15 13:30:36 2015] dead process: id="7074732f31000000" pid="7717"

Does that help you?

He also mentioned, and I paraphrase: It might be easier to #ifdef USER_PROCESS instead of #ifndef UTMP_HAS_NO_TYPE because maybe the current #ifdef only tests whether utmp::ut_type is present -- not utmpx::ut_type. Also, the kill loops is a bit suspect, because if someone forgets to set ut_pid, net-snmp will garbage collect them even though it should leave them alone. I don't know of a single system that does implement getutent() and friends, but does not implement getutxent(). So it might be worth patching it up to use utmpx exclusively.

Last edit: Dan Langille 2015-08-17

If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
- Bill Fenner - 2015-08-18
  
  UTMP_HAS_NO_TYPE is left over from the pre-autoconf configuration system. It's pretty awesome:
  
  freebsd10.h:#include "freebsd9.h" freebsd2.h:#include "freebsd.h" freebsd3.h:#include "freebsd.h" freebsd4.h:#include "freebsd.h" freebsd5.h:#include "freebsd4.h" freebsd6.h:#include "freebsd5.h" freebsd7.h:#include "freebsd6.h" freebsd8.h:#include "freebsd7.h" freebsd9.h:#include "freebsd8.h" freebsd.h:#include "bsd.h"
  
  and bsd.h, of course, has:
  
  #define UTMP_HAS_NO_TYPE 1 #define UTMP_HAS_NO_PID 1
  
  since that was probably true of 4.2BSD.
  
  So, your problem is that net-snmp is ignoring the ut_type field.
  
  I agree that net-snmp shouldn't be updating utmp based on killing the process, but that's compiled out on FreeBSD since it also "has no pid" there ;-)
  
  Bill
  
  If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
  - Dan Langille - 2015-08-18
    
    Ahh, yes, the #ifdef lines 682-686.
    
    are you suggesting this patch:
    
```shell
@@ -16,5 +16,5 @@
*/
#define ARP_SCAN_FOUR_ARGUMENTS 1

-#define UTMP_HAS_NO_TYPE 1
+#define UTMP_HAS_NO_TYPE 0
#define UTMP_HAS_NO_PID 1
```
    
    If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
    - Bill Fenner - 2015-08-18
      
      It's #ifdef, not #if, so the right fix is to #undef UTMP_HAS_NO_TYPE in freebsdN.h after the include of bsd.h, where N is the version in which ut_type was introduced. (Or the most recent version that anyone shuold be allowed to care about, e.g., I'd be fine with N=8)
      
      When I try to think about the real fix I tend to think about autoconf'ing the world and then my brain starts to hurt :-)
      
      If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
      - Dan Langille - 2015-08-20
        
        What testing can I do on my systems to help?
        
        If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
        
        Bill Fenner - 2015-08-25
        
        Can you rebuild with
        
        #undef UTMP_HAS_NO_TYPE
        
        in freebsd8.h (after it #includes freebsd7.h) and test the value reported by the daemon?
        
        If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
        
        Dan Langille - 2015-08-25
        
        Before installing patched snmpd:
        
        $ snmpwalk -v3 -l authPriv -u rodvl -a SHA -A AuthPass -x AES -X PrivPass varm.int.unixathome.org HOST-RESOURCES-MIB::hrSystemNumUsers.0
        HOST-RESOURCES-MIB::hrSystemNumUsers.0 = Gauge32: 4
        
        After installing patched snmpd:
        
        $ snmpwalk -v3 -l authPriv -u rodvl -a SHA -A AuthPass -x AES -X PrivPass varm.int.unixathome.org HOST-RESOURCES-MIB::hrSystemNumUsers
        HOST-RESOURCES-MIB::hrSystemNumUsers.0 = Gauge32: 1
        
        After logging out of the target machine:
        
        $ snmpwalk -v3 -l authPriv -u rodvl -a SHA -A AuthPass -x AES -X PrivPass varm.int.unixathome.org HOST-RESOURCES-MIB::hrSystemNumUsers
        HOST-RESOURCES-MIB::hrSystemNumUsers.0 = Gauge32: 0
        
        If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
        
        Dan Langille - 2015-08-25
        
        Patch at https://gist.github.com/dlangille/dc1bccfe046a283579b5
        
        If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
        
        Dan Langille - 2015-08-25
        
        The proof is in the pudding.
        
        Last edit: Dan Langille 2015-08-25
        
        Screen Shot 2015-08-25 at 3.36.50 PM.png
        
        If you would like to refer to this comment somewhere else in this project, copy and paste the following link:

Bill Fenner - 2015-09-11

I've checked in a patch to the 5.7 and master branches. Would you mind pulling HEAD from one of these and building to make sure things are OK?

I've #undef'd both NO_TYPE and NO_PID, but I've also removed the code that writes to utmp - it just skips PIDs that we can't kill.

If you would like to refer to this comment somewhere else in this project, copy and paste the following link:

Dan Langille - 2015-10-16

I'm going to try this now.

If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
- Dan Langille - 2015-10-16
  
  My plan was to find the commit, apply it to my local tree, and try it out. But I can't find the commit, or where to download a branch....
  
  If you would like to refer to this comment somewhere else in this project, copy and paste the following link:

Dan Langille - 2015-10-16

Ahhh Oh there it is... https://sourceforge.net/p/net-snmp/code/ci/master/tree/

If you would like to refer to this comment somewhere else in this project, copy and paste the following link:

Dan Langille - 2015-10-16

All seems well, just a few minutes after upgrading, the correct number of users is being displayed.

Bill: to be sure I applied the correct patch,

I also think we need check the other values, which seem high to me:

context switches 7.5 M
interrupts 7.5 M
swap I/O activity 40G

see graphs at https://twitter.com/DLangille/status/655152494671216640

If you would like to refer to this comment somewhere else in this project, copy and paste the following link:

Dan Langille - 2015-10-16

FYI, it did not build on i386 and I have not investigated that yet: http://services.unixathome.org/poudriere/build.html?mastername=102i386-default-master-list-i386&build=2015-10-16_22h48m37s

If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
- Bill Fenner - 2015-10-19
  
  Ugh? checking size of short... Segmentation fault (core dumped). Any way to access the config.log from that run?
  
  If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
  - Dan Langille - 2015-10-19
    
    Attached...
    
    config.log
    
    If you would like to refer to this comment somewhere else in this project, copy and paste the following link:

HOST-RESOURCES-MIB::hrSystemNumUsers.0 returns wrong number of users

Group

Searches

Help

#2658 HOST-RESOURCES-MIB::hrSystemNumUsers.0 returns wrong number of users

Discussion