Mongo binaries are -
mongodb-linux-x86_64-enterprise-rhel62-2.6.4.tar.gz installed on x86-64 box.
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OS Red Hat linux -
$ uname -a
Linux 2.6.18-398.el5 x86_64
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Mongo configuration file in YAML format.

daycare2:/dbahome/mongo/configs >
$ cat t0lab.conf
net:
bindIp: 10.250.114.71
port: 29000
processManagement:
fork: true
storage:
dbPath: /data/db/mongo_inst0/t0lab
directoryPerDB: true
smallFiles: true
journal:
enabled: true

systemLog:
destination: file
timeStampFormat: iso8601-local
logAppend: false
path: /msglog/mongo_inst0/msg.log
quiet: true
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Error on attempt to start mongo instance

daycare2:/ >
$ mongod -f /dbahome/mongo/configs/t0lab.conf
mongod: error while loading shared libraries: libnetsnmpagent.so.20: cannot open shared object file: No such file or directory

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daycare2:/dbahome/mongo >
$ cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5.11 (Tikanga) <= release of Linux on daycare2.
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$ rpm -qa |grep snmp <= determines all rpm packages with the name snmp that are installed on the box.
net-snmp-libs-5.3.2.2-25.el5_11
net-snmp-5.3.2.2-25.el5_11
net-snmp-utils-5.3.2.2-25.el5_11
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[root@daycare2 ~]# rpm -ql net-snmp-libs |grep snmp <= to see what is in the package
/usr/lib64/libnetsnmp.so.10
/usr/lib64/libnetsnmp.so.10.0.3
/usr/lib64/libnetsnmpagent.so.10
/usr/lib64/libnetsnmpagent.so.10.0.3
/usr/lib64/libnetsnmphelpers.so.10
/usr/lib64/libnetsnmphelpers.so.10.0.3
/usr/lib64/libnetsnmpmibs.so.10
/usr/lib64/libnetsnmpmibs.so.10.0.3
/usr/lib64/libnetsnmptrapd.so.10
/usr/lib64/libnetsnmptrapd.so.10.0.3
/usr/lib64/libsnmp.so.10
/usr/lib64/libsnmp.so.10.0.3
/usr/lib/libnetsnmp.so.10
/usr/lib/libnetsnmp.so.10.0.3
/usr/lib/libnetsnmpagent.so.10
/usr/lib/libnetsnmpagent.so.10.0.3
/usr/lib/libnetsnmphelpers.so.10
/usr/lib/libnetsnmphelpers.so.10.0.3
/usr/lib/libnetsnmpmibs.so.10
/usr/lib/libnetsnmpmibs.so.10.0.3
/usr/lib/libnetsnmptrapd.so.10
/usr/lib/libnetsnmptrapd.so.10.0.3
/usr/lib/libsnmp.so.10
/usr/lib/libsnmp.so.10.0.3

so appears we do not have the libnetsnmp.so.20 file in RHEL 5.11
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$ rpm -ql net-snmp-libs-5.5-49.el6_5.4.x86_64 |grep -i libnetsnmp
/usr/lib64/libnetsnmp.so.20 <= seems like present in a higher version of net-snmp-libs e.g. RHLinux 6+

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The mongo website says RH linux 5.6 is supported so why this problem ? how do we obtain net-snmp-libs-5.5-49.el6_5.4.x86_64 for RHEL 5.6 ? or is the issue because of some other problem ?