http://www.linuxblog.org Linux server and open source blog Tue, 19 Aug 2008 05:55:17 +0000 http://backend.userland.com/rss092 en Some Centos users are complaining about the following error when executing SUDO: audit_log_user_command(): Connection refused However, this is nothing to worry about. Centos kernel doesn't have this feature enabled for audit and this is why it's complaining. For example, Fedora has compiled this feature into own kernel and no problems are reported. ... http://www.linuxblog.org/audit_log_user_command-connection-refused/ We have seen great performance on using ReiserFS for mail system spools and in our tests ReiserFS file system spool for Postfix queues was very fast. For best performance we used notail, noatime mount options in /etc/fstab file. Full example: /dev/sda2/usr reiserfs notail,noatime,rw,auto 0 0 notatime - turns off atimes calls, reduces IO and ... http://www.linuxblog.org/reiserfs-for-scalable-and-high-load-smtp-servers/ If you run a busy DNS server or any other service that uses a lot of UDP traffic, it's possible that your default Iptable conntrack sessions (connection tracking entries in kernel memory) settings are too low and netfilter is unable to track all your sessions. The error is usually something like ... http://www.linuxblog.org/iptable-ip_conntrack-table-set-up-and-tunning-for-high-load-udp-traffic/ The settings for sysctl.conf below apply for Fedora, RedHat, Centos OS as well as other Linux flavors. These settings will improve your server network stack and some little protection against ddos attacks as well. Feel free to improve as you wish :) # Kernel sysctl configuration file for Red Hat Linux # # ... http://www.linuxblog.org/improving-linux-network-stack/