Upgrading ReplicaSet from 2.2.2 to 2.4.1 on Ubuntu 12.04_LTS. Upgrading one secondary at a time and then stepDown primary and upgrade it. After upgrading one of the secondaries, the other secondary (2.2.2) became the primary. So far so good. At the same time the one just upgraded to 2.4.1 crashed and asked for a forced restart. The forced restart made the server come back. Here´s the trace log: Wed Apr 10 19:13:42.892 [conn11018514] authenticate db: mobile-ads { authenticate: 1, user: "heroku_app", nonce: "c4f142c96e76b192", key: "e3da736a5915cc8fd221c9f0e1055f88" } Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Invalid access at address: 0x7ed6ab13bff0 from thread: conn11018521 Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Invalid access at address: 0x7ed6b0386ff0 from thread: conn11018523 Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Invalid access at address: 0x7ed6b088bff0 from thread: conn11018532 Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Invalid access at address: 0x7ed6ae06aff0 from thread: conn11018525 Invalid access at address: 0x7ed6aec76ff0 from thread: conn11018530 Invalid access at address: 0x7ed6ae16bff0 from thread: conn11018524 Wed Apr 10 19:13:42.961 Invalid access at address: 0x7ed6adf69ff0 from thread: conn11018526 Invalid access at address: 0x7ed6ade68ff0 from thread: conn11018527 Wed Apr 10 19:13:42.961 Invalid access at address: 0x7ed6af57fff0 from thread: conn11018531 Invalid access at address: 0x7ed6ae46eff0 from thread: conn11018520 Invalid access at address: 0x7ed6b0689ff0 from thread: conn11018529 Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Got signal: 11 (Segmentation fault). Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.961 Got signal: 11 (Segmentation fault). Invalid access at address: 0x7ed6aea74ff0 from thread: conn11018522 Invalid access at address: 0x7ed6add67ff0 from thread: conn11018528 Wed Apr 10 19:13:42.961 Got signal: 11 (Segmentation fault). Got signal: 11 (Segmentation fault). Wed Apr 10 19:13:42.961 Got signal: 11 (Segmentation fault). Wed Apr 10 19:13:42.961 Wed Apr 10 19:13:42.962 Got signal: 11 (Segmentation fault). Got signal: 11 (Segmentation fault). Got signal: 11 (Segmentation fault). Got signal: 11 (Segmentation fault). Wed Apr 10 19:13:42.961 Got signal: 11 (Segmentation fault). Invalid access at address: 0x7ed6ae56fff0 from thread: conn11018519 Got signal: 11 (Segmentation fault). Wed Apr 10 19:13:42.962 Got signal: 11 (Segmentation fault).