Не знаю, как на Юбунтуе, но на дебиане от которого она произошла работает примерно так:
#/etc/defaults/snmpd
# This file controls the activity of snmpd and snmptrapd
# MIB directories. /usr/share/snmp/mibs is the default, but
# including it here avoids some strange problems.
export MIBDIRS=/usr/share/snmp/mibs
# snmpd control (yes means start daemon).
SNMPDRUN=yes
# snmpd options (use syslog, close stdin/out/err).
SNMPDOPTS='-Lsd -Lf /dev/null -u snmp -I -smux -p /var/run/snmpd.pid'
# snmptrapd control (yes means start daemon). As of net-snmp version
# 5.0, master agentx support must be enabled in snmpd before snmptrapd
# can be run. See snmpd.conf(5) for how to do this.
TRAPDRUN=no
# snmptrapd options (use syslog).
TRAPDOPTS='-Lsd -p /var/run/snmptrapd.pid'
# create symlink on Debian legacy location to official RFC path
SNMPDCOMPAT=yes
На соседней машине стартует так:
/usr/local/sbin/snmpd -p /var/run/snmpd.pid
ЗЫ: а вообще, зри в фаерволл - может проблема именно там.