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Showing posts from December, 2009

SED-Replace multiple lines with a single line

A useful option of sed command to replace multiple lines with a single line upon matching a given string. $ cat -n file.txt Hello world Hello nobody nobody Somebody anybody If you want to replace the lines 2 and 3 with another line "Hello everybody" the below command will help. $ sed '/nobody$/{N;s/Hello nobody\nnobody/Hello everybody/}' file.txt $ cat -n file.txt 1 hello world 2 Hello everybody 3 Somebody 4 anybody

SMTP authentication through TELNET

It's common that we use TELNET to port 25 of Mail server to check the connectivity and to ensure the Mail flow. It's also possible to perform SMTP authentication in TELNET session $ telnet yourmailserver 25 type “HELO”, hit Enter. AUTH LOGIN Now you have to enter your email ID and then your password encoded in BASE64. For converting your email and password to Base64 use the conversion tools at WebPan or Ostermiller Reference KongTechnology

echo colourfully

# for i in `cat num.txt`; do echo -en '\E[3'$i'm'"\033[1mPsycho Tux\033[0m " ; done; # for i in `cat num.txt`; do echo -en '\E[47;3'$i'm'"\033[1mPsycho Tux\033[0m " ; done; # cat num.txt 1 2 3 4 5 6 7 8 9 0

Block direct SSH to root, but not to root equivalent

The PermitRootLogin no option of /etc/ssh/sshd_config will block all the users with UID 0. Below is an option to overcome this. # vi /etc/ssh/sshd_config ###PermitRootLogin no AllowUsers newuser guest psychotux hari DenyUsers root # /etc/init.d/sshd restart Here users listed along with AllowUsers can be normal user or root equivalent.

Hardware clock failure in ISA system

In ISA systems /sbin/hwclock will fail to fetch the Hardware clock and will throw an error similar to below. # hwclock select() to /dev/rtc to wait for clock tick timed out # hwclock --show select() to /dev/rtc to wait for clock tick timed out But the --directisa option of hwclock will work here. # /sbin/hwclock --directisa So as a permanent solution we can rename the existing binary /sbin/hwclock and create a new Wrapper as below 1. Find the version of hwclock # hwclock --version 2. Rename the binary by suffixing the version number # cd /sbin # mv hwclock hwclock-x.y 3. Create a wrapper for the hwclock-x.y named hwclock # cat > hwclock << HERE #!/bin/bash /sbin/hwclock-x.y --directisa \$@ HERE 4. Give necessary execute permission and reboot the server # chmod +x hwclock 5. Check the hardware clock, System Time, NTP, etc. To synchronize system time with Hardware clock we can use hwclock --hctosys And an optional reboot # reboot