Create a sitemap

http://www.xml-sitemaps.com/
http://www.dmoz.org/Computers/Internet/Searching/Search_Engines/Sitemaps/

Pulseaudio Preferences (paprefs)

yum install paprefs

svn undo last change

Suppose we want to undo the last ci (revision 100) back to 99 for the changes in current directory.

svn merge --revision 100:99 .

or

svn merge -c -100

Apache2 mod_rewrite module

The environment variables and syntax are documented here. $N are the regexp matches on RewriteRule and %N are the ones from RewriteCond.

Apache2 mod_cache

The setup instructions can be found here. However, I noticed my CacheRoot is always empty. After I turned on Loglevel debug. I notice there was a permission problem "mod_cache.c: (13)Permission denied". Just have to make the permission corrent and it then worked...

# chown apache.apache /tmp/cache/httpd/
# chcon -t httpd_sys_content_t /tmp/cache/httpd/ 

Apache2 Connection Timeout

Sometimes I can not connect to my server, I found out that it is related to net.ipv4.tcp_tw_recycle=1. I do not understand why as this is recommended setting for server....

Here says it should be disabled http://kbase.redhat.com/faq/FAQ_80_6180.shtm

Enable mod_dumpio on Apache2

Use the following configuration:

LoadModule dumpio_module modules/mod_dumpio.so
LogLevel debug
DumpIOInput On
DumpIOOutput On
#DumpIOLogLevel can be set optionally
#DumpIOLogLevel debug

Check Apache2 Config Syntax

# httpd -t
Syntax OK

tcpdump http traffic

tcpdump  -s 0 -i eth0 dst or src host mydomain.com  and port 80
tcpdump  -A -s 0 -i eth0 dst or src host mydomain.com  and port 80

other commands

tcpdump src 192.168.11.200
tcpdump src 192.168.11.200 and port tftp
tcpdump -n dst 192.168.11.1 and udp
tcpdump -n dst 192.168.0.1 or  dst 192.168.0.10 and udp # display ip
tcpdump -nn dst 192.168.0.1 or  dst 192.168.0.10 and udp # display both ip and port
tcpdump -nn ip multicast  and not broadcast

see also http://www.rationallyparanoid.com/articles/tcpdump.html

Free DNS server

http://theos.in/windows-xp/free-fast-public-dns-server-list/

Slow ssh login

Originally, I thought it was the sshd DNS configuration (i.e. UseDNS) which is already set to no. It turns out that the first domain server in /etc/resolv.conf on the server is slow. After switching the order of the servers, ssh become fast again... This is related to the entries I added to hosts.deny.

Add SSL Certificate from Startcom to Apache

Get free certificates(3 files) from Startssl.com and modify the following:

SSLCertificateFile /etc/pki/tls/certs/mydomain.com.crt      #generated by startcom
SSLCertificateKeyFile /etc/pki/tls/private/mydomain.com.key #generated by startcom
SSLCACertificateFile /etc/pki/tls/certs/startcom.bundle.crt #downloaded from startcom

Assign Multiple IP's on Single NIC

Restart the network after creating the following file:

# cat /etc/sysconfig/network-scripts/ifcfg-eth0-range0 
IPADDR_START=192.168.1.2
IPADDR_END=192.168.1.3
CLONENUM_START=0

Reverse DNS Lookup

Use nslookup or host command:

nslookup ipaddr
host ipaddr

tcpwrapper: hosts.allow / hosts.deny

hosts.allow will overide hosts.deny.
Below is a configuration I use for my home computer that can not be connected directly from outside:

hosts.allow:
sshd: 192.168.0.0/255.255.255.224 except 192.168.0.1
hosts.deny:
sshd: ALL

The Below is a machine that can be connected from outside:

hosts.allow:
sshd: 192.168.0.0/255.255.255.224 except 192.168.0.1
hosts.deny:
sshd: PARANOID,UNKNOWN
sshd: *.com.mx,*.com.ar,*.it, *.ro

ssh session stuck

press ~ tehn . to send a break/recover.

Redirect kern.warn iptables log

add the following lines to /etc/syslog.conf

kern.warning /var/log/iptables.log

Configuring Postfix with SASL

See Postfix SASL Howto and www.mysql-apache-php.com/.

This is for CentOS 4 http://www.hughesjr.com/content/view/14/29/

Here is another one with TLS http://wiki.centos.org/HowTos/postfix_sasl

When using TLS for postfix, make sure master.cf has

smtps     inet  n       -       n       -       -       smtpd
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_tls_wrappermode=yes

Configure Squirrelmail

Change domain in /etc/squirrelmail/config.php:

$domain = 'mydomain.com';

so the email received will have user@mydomain.com

To use https on apache, add the following to /etc/httpd/conf.d/squirrelmail.conf:

<Location /webmail>RewriteEngine on
RewriteCond %{HTTPS} !=on
RewriteRule .* https://%{HTTP_HOST}:443%{REQUEST_URI} [QSA,R=permanent,L]
</Location>

Finally, selinux settings:

setsebool -P httpd_can_network_connect=1

Dovecot Imaps Server setup

You can do this for pop/pops/imap as well, here I only wanted to configure imaps. Make the following changes to /etc/dovecot.conf:

protocols = imaps
login_process_size = 64  # for x86_64
imap_client_workarounds = delay-newmail outlook-idle netscape-eoh

.
Also remember to open the port 993 for imaps in the iptable configuration.

Configure postfix

If this is a web server, make sure you changed MX record with dns provider to point to your server (or you will not be able to receive mail). I have modified the following is /etc/postfix/mail.cf:

myhostname = mydomain.com
myorigin = $myhostname
inet_interfaces = all
mydestination = $myhostname, localhost.$mydomain, localhost

Use http://pingability.com to check your DNS setup.

Free Unix Account

You can get a temporary unix account by

telnet sdf.lonestar.org

Though this you can not telnet out out the box. For that, you can try http://www.bshellz.net/register

Tunnel VNC over ssh

This will be faster than using VNC over X over ssh (i.e., ssh -X). Let us say we want to tunnel vnc from remote to local and the vncserver on remote is started on port 2 (5092).

local$ ssh -C -L 5902:127.0.0.1:5902  uid@remote

Then on remote start vncserver if it is not started

remote$ vncserver :2

Now on start vncviewer on local to connect to remote vnc server:

local$ vncviewer locathost:2

X over ssh

Use either -X or -Y option with ssh.

localhost$ ssh -X remotehost
remotehost$ xterm     # this remotehost xterm will show on your local machine

svn ignore a file

The property is set on a directory. Below I created a file abc.txt and set svn:ignore on it:

$ touch abc.txt
$ svn propset svn:ignore abc.txt .
property 'svn:ignore' set on '.'
$ svn propget svn:ignore .
abc.txt

$ svn status --no-ignore
I      abc.txt
 M     .

Add with an editor:

svn propedit svn:ignore .

Ssh Read from remote host remote.com: Connection reset by peer

My hosting company firewall seems to drop idle connections. When I do a who on the server, there are many ssh sessions that are already dropped on the client side. I add the following to the /etc/ssh/sshd_config, then restarted the sshd. Connection reset does not happen anymore. Had to adjust ClientAliveInterval a few times to half of the firewall's timeout value.

TCPKeepAlive yes
ClientAliveInterval 240

Also you can change this in the kernel:

# cat /proc/sys/net/ipv4/tcp_keepalive_time
7200
# echo 240 > /proc/sys/net/ipv4/tcp_keepalive_time

And make changes to /etc/sysctl.conf permanently.

net.ipv4.tcp_keepalive_time = 180

svn 1.4 compression

SVN 1.4 has compression support (use ldd to see if it is linked with libz). If use svn+ssh, enable ssh compression actually slows down the svn in my tests.

ldd /usr/bin/svn
...
libz.so.1 => /lib64/libz.so.1 (0x0000000020802000)
... 

groupadd and useradd

Add a group 'friend' with a specific gid 600:

groupadd --gid 600 friend

Create a user with a specific gid 'friend':

useradd -g friend -m username

Add a existing user 'username' to a group 'friend'

usermod -a -G friend username

Change username's primary group to 'friend'

 usermod -g friend username