Oracle DBA & Unix Skills : Two Sides Of The Same Coin (Part-I)

Following Unix snippet will remove ^M character from all the files in the current directory.
This will come handy when the OS does not have dos2unix command.
for file in *
do
tr -s "\r" "\n" < $file > temp_file
mv temp_file $file
done
----------------------------------------------------------------------------------------------------------------
Following command will show which process(PID) is using port 1521

$ lsof -i tcp:1521|grep -i Listen
tnslsnr 8757722 oracle 8u IPv4 0xf10006000b072b98 0t0 TCP server125_vip.mylab.com:ncube-lm (LISTEN)
tnslsnr 8757722 oracle 10u IPv4 0xf100060008425398 0t0 TCP server125.mylab.com:ncube-lm (LISTEN)

----------------------------------------------------------------------------------------------------------------
Following command will print the routing table on the host. Useful for troubleshooting network issues, especially "Destination Host Unreachable" when the routes are incorrectly defined.
$ netstat -nr
Routing tables
Destination Gateway Flags Refs Use If Exp Groups

Route tree for Protocol Family 2 (Internet):
default 172.22.1.65 UGA 73 93805232 en4 - -
10.207.0.0 10.207.1.35 UHSb 0 0 en2 - - =>
10.207/20 10.207.1.35 U 3 2662434 en2 - -
10.207.1.35 127.0.0.1 UGHS 0 9480 lo0 - -
10.207.15.255 10.207.1.35 UHSb 2 76697 en2 - -
127/8 127.0.0.1 U 6 265726 lo0 - -
172.22.1.64 172.22.1.83 UHSb 0 0 en4 - - =>
172.22.1.64/26 172.22.1.83 U 59 85149714 en4 - -
172.22.1.83 127.0.0.1 UGHS 79 321272333 lo0 - -
172.22.1.127 172.22.1.83 UHSb 0 1 en4 - -
192.168.61.13 172.22.1.80 UGH 0 33543933 en4 - - =>
192.168.61.13/32 172.22.1.80 UG 0 0 en4 - -
192.168.61.14 172.22.1.82 UGH 0 575 en4 - -
194.10.159.9/32 10.207.0.12 UG 0 63056789 en2 - -

Route tree for Protocol Family 24 (Internet v6):
::1 ::1 UH 0 0 lo0 - -

----------------------------------------------------------------------------------------------------------------
SSH Login : Playing Dirty

When you login with ssh (port 22) or using putty to a unix server, the server allocates a pseudo-tty.
Then we provide the username and password (login credentials). Once after successful login test this
who (this will show you who all are logged in)
$ who
slodam pts/0 Dec 20 15:35 (167.210.219.37)
applmgr pts/1 Nov 21 09:22
oracle pts/2 Nov 16 10:53

Note that who command shows your IP address and the login name.

Now, try to sneak in to the unix server using ssh -T username@password
$ ssh -T slodam@...
slodam@...'s password:
who
applmgr pts/1 Nov 21 09:22
oracle pts/2 Nov 16 10:53

hostname command shows server126
Press Ctl+C to terminate the ssh session.

Now, nobody knows that you are logged in. Nobody knows what is your IP.

ssh -T disables pseudo-tty allocation. Since no terminal exists for you sneaked
login no information can be found about your session.


Thanks for reading
Satish Lodam