Linux Configure Netconsole To Log Messages Over UDP Network

Posted on in Categories CentOS, Debian Linux, File system, FreeBSD, Gentoo Linux, GNU/Open source, Hardware, kernel, Linux, Linux distribution, Linux Log Management, Security, Sys admin, Tips, Troubleshooting, Ubuntu Linux last updated July 2, 2008

Linux netconsole kernel module allows dmesg output to be transmitted via the syslogd network. It is kernel-level network logging over udp allowing debugging of problem where disk logging fails and serial consoles are impractical. This is a step-by-step mini howto about netconsole configuration under Red Hat, CentOS, Fedora and Debian Linux.

Logging to a centralized loghost from Router or other hosts

Posted on in Categories Backup, CentOS, Debian Linux, Howto, Linux, UNIX, Windows server last updated February 16, 2006

It is really a good idea to have one central logging host for security and performance reason. For example monitoring log files will help you to detect:
* Security risks (you can see failed login attempt, port scan etc) analysis
* Troubleshoot user login problem
* Save disk space
* If hard disk crashed on other hosts old logs will be available from centralized loghost

Linux (and other UNIX like systems) use sysklogd (or syslogd) utility. It is system logging facility. It support of both internet and unix domain sockets enables this utility package to support both local and remote logging from DSL/ADSL router or other hosts in your network.

Prepare syslogd to accept remote logging message

Open file /etc/init.d/sysklogd under Debian Linux to configure syslogd to accept remote message.
# vi /etc/init.d/sysklogd
Locate line SYSLOGD and edit it as follows:
SYSLOGD="-r"
The option (-r) will enable the facility to receive message from the network using an internet domain socket with the syslog service. The default is to not receive any messages from the network.

Save file and exit to shell prompt. Restart the sysklogd:
# /etc/init.d/sysklogd restart

A note about RHEL / CentOS / Fedora Linux User

If you are using Red Hat or Fedora Linux, edit file /etc/sysconfig/syslog:
# vi /etc/sysconfig/syslog
Make changes:
SYSLOGD="-r"
Restart syslogd:
# service syslog restart

Open UDP port 514

If you are, using iptables based firewall, insert following rule to your iptables script to accept connection from your network:

MYNET=192.168.1.0/24
SLSERVER=192.168.1.100

iptables -A INPUT -p udp -s $MYNET --sport 1024:65535 -d $SLSERVER --dport 514 -m state --state NEW,ESTABLISHED -j ACCEPT

iptables -A OUTPUT -p udp -s $SLSERVER --sport 514 -d $MYNET --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT

192.168.1.100 is IP address of syslogd server. You need to restrict access to syslogd within your network (192.168.1.0/24) only.

Configure the Router to logging message to a centralized loghost

You can open web configuration interface and type IP address of centralized loghost (192.168.1.100) and port 514. Save configuration and reboot router.

Configure Linux or Unix host to logging message to a centralized loghost

You need to open syslog configuration file /etc/syslog.conf:
# vi /etc/syslog.conf
Setup syslogd to send all important message related to auth to loghost IP 192.168.1.100 (or use FQDN if configured)

*.*;auth,authpriv.none          @192.168.1.100

OR

*.*;auth,authpriv.none          @loghost.mydomain.com.

Restart sysklogd (Debian Linux):
# /etc/init.d/sysklogd restart
OR
Restart syslogd under Red Hat/Fedora / CentOS Linux
# service syslog restart
If required open outgoing UDP 514 port from other hosts:

# SYSLOG outgoing client request
iptables -A OUTPUT -p udp -s 192.168.1.100 --sport 1024:65535 -d 192.168.1.5 --dport 514 -m state --state NEW,ESTABLISHED -j ACCEPT

iptables -A INPUT -p udp -s 192.168.1.5 --sport 514 -d 192.168.1.100 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT

Windows NT/2000/XP/Vista Desktop system

You can force your Windows NT/2000/XP desktop to log all messages to a centralized loghost. However, Windows do not have in build system to log message to remote Unix syslogd server. You can use NTsyslog program, which runs as a service under Windows NT based operating systems. It formats all System, Security, and Application events into a single line and sends them to a syslogd host.

Verify that message are logged in to your /var/log/messages# tail -f /var/log/messages
Output:

Feb 16 02:08:01 router  kernel: klogd started: BusyBox v1.00 (2005.09.22-19:11+0000)
Feb 16 02:08:01 router  kernel: Linux version 2.6.8.1 (root@localhost.localdomain) (gcc version 3.4.2) #1 Thu Sep 22 15:07:47 EDT 2005
Feb 16 02:08:01 router  kernel: Total Flash size: 2048K with 39 sectors
Feb 16 02:08:01 router  kernel: 96338L-2M-8M prom init
Feb 16 02:08:01 router  kernel: CPU revision is: 00029010
Feb 16 02:08:01 router  kernel: Determined physical RAM map:
Feb 16 02:08:01 router  kernel:  memory: 007a0000 @ 0000000
..........
...
......
Feb 16 02:08:01 router  kernel: AdslCoreHwReset: AdslOemDataAddr = 0xA07E504C
Feb 16 02:08:01 router  kernel: ip_tables: (C) 2000-2002 Netfilter core team
Feb 16 02:08:01 router  kernel: ip_conntrack version 2.1 (61 buckets, 0 max) - 368 bytes
Feb 16 02:08:06 router  pppd[224]: pppd 2.4.1 started by admin, uid 0
Feb 16 02:08:07 router  pppd[224]: PPP: Start to connect ...
Feb 16 02:08:10 router  dnsprobe[272]: dnsprobe started!

How to: FreeBSD Setup Time / Clock Synchronization with NTP server and ntpdate command

Posted on in Categories FreeBSD, Howto, Sys admin, Tips, UNIX last updated January 25, 2006

FreeBSD use the Network Time Protocol (NTP) for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. NTP uses UDP port 123. If you have one computer or single server then you can easily synchronization time with other NTP servers. All you need is ntp client called ntpdate. It is use to set the date and time via NTP servers.

FreeBSD: Install NTP Client

Use any one of the following command to install NTP:

# pkg_add -rv  ntp

OR

# cd /usr/ports/net/ntp
# make; make install

Pick appropriate NTP Servers

Visit public ntp timeserver list to pick up your NTP server.

Open UDP port 123 at firewall

If you are running FreeBSD ipfilter firewall, you need to open the UDP port 123. Just add following rule to your firewall script:

pass out quick on lnc0 proto udp from YOUR-SERVER to any port = 123
keep state

OR

pass out quick on lnc0 proto udp from YOUR-SERVER to
TIME-SERVER-IP port = 123 keep state

For example, my FreeBSD workstation IP is 192.168.1.16 and 61.246.176.131 is IP of NTP server then my rule is in ipf.conf file as follows:

pass out quick on lnc0 proto udp from 192.168.1.16
to 61.246.176.131 port = 123 keep state

FreeBSD test clock synchronization

Just run ntpdate command as follows to see you can set date and clock via NTP:
Set wrong date (Mon Dec 13 4:27 pm):

# date 0412131627

Now set correct date with ntp client:

# ntpdate -v -b in.pool.ntp.org

13 Dec 16:27:50 ntpdate[997]: ntpdate 4.2.0-a Thu Nov 3 07:34:22 UTC 2005 (1)
25 Jan 12:35:47 ntpdate[997]: step time server 61.246.176.131 offset 35237275.965726 sec

You can verify that correct data is setup:

# date

Output:

Wed Jan 25 12:36:21 IST 2006

Enable date and time/ clock Synchronization at boot time

You need to set ntpdate via /etc/rc.local file.

# vi /etc/rc.conf

Append following line to it:
ntpdate_enable="YES"
ntpdate_hosts="asia.pool.ntp.org"

Save and close the file. Make sure you have correct ntpdate_hosts server entry.

See also:

Updated for accuracy.

Linux Iptables block or open DNS / bind service port 53

Posted on in Categories BIND Dns, Debian Linux, Gentoo Linux, Howto, Iptables, Linux, Networking, RedHat/Fedora Linux, Security, Suse Linux, Tips, Troubleshooting last updated July 13, 2005

The domain name service provided by BIND (named) software. It uses both UDP and TCP protocol and listen on port 53. DNS queries less than 512 bytes are transferred using UDP protocol and large queries are handled by TCP protocol such as zone transfer.

i) named/bind server – TCP/UDP port 53

ii)Client (browser, dig etc) – port > 1023

Allow outgoing DNS client request:

Following iptables rules can be added to your shell script.

SERVER_IP is your server ip address

DNS_SERVER stores the nameserver (DNS) IP address provided by ISP or your own name servers.

Following rules are useful when you run single web/smtp server or even DSL/LL/dialup Internet connections:

SERVER_IP="202.54.10.20"
DNS_SERVER="202.54.1.5 202.54.1.6"
for ip in $DNS_SERVER
do
iptables -A OUTPUT -p udp -s $SERVER_IP --sport 1024:65535 -d $ip --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p udp -s $ip --sport 53 -d $SERVER_IP --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT
iptables -A OUTPUT-p tcp -s $SERVER_IP --sport 1024:65535 -d $ip --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -p tcp -s $ip --sport 53 -d $SERVER_IP --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT
done

(B) Allow incoming DNS request at port 53:

Use following rules only if you are protecting dedicated DNS server.

SERVER_IP is IP address where BIND(named) is listing on port 53 for incoming DNS queries.

Please note that here I’m not allowing TCP protocol as I don’t have secondary DNS server to do zone transfer.

SERVER_IP="202.54.10.20"
iptables -A INPUT -p udp -s 0/0 --sport 1024:65535 -d $SERVER_IP --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p udp -s $SERVER_IP --sport 53 -d 0/0 --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT
iptables -A INPUT -p udp -s 0/0 --sport 53 -d $SERVER_IP --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p udp -s $SERVER_IP --sport 53 -d 0/0 --dport 53 -m state --state ESTABLISHED -j ACCEPT

Please note if you have secondary server, add following rules to above rules so that secondary server can do zone transfer from primary DNS server:

DNS2_IP="202.54.10.2"
iptables -A INPUT -p tcp -s $DNS2_IP --sport 1024:65535 -d $SERVER_IP --dport 53 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -s $SERVER_IP --sport 53 -d $DNS2_IP --dport 1024:65535 -m state --state ESTABLISHED -j ACCEPT