Site for admins about operating systems and security
How to transparently redirect HTTP requests on port 80 to a http proxy on port 8080?
By using the iptable nat
First pre-requisite is enabling IP forwarding on the system
#echo “net.ipv4.conf.all.forwarding =1”>>/etc/sysctl.conf && sysctl -p
Then issue the below iptable command
#iptables -t nat -A PREROUTING -p tcp –dport 80 -j REDIRECT –to-port 8080
I have installed CentOS minimal and the commands, ifconfig, netstat and traceroute are not recognized: how come?
These are considered now deprecated or legacy commands/utilities, please get more info on their equivalent (in the order):
ip
ss
tracepath
How can I add a volume in a raid?
#mdadm –manage /dev/md0 –add /dev/sdd1
How do I display a substring of a variable in bash?
For example, you want to display the first seven characters from a string passed from the command line
echo ${$1:0:7}
Of course you can also save the value somewhere
substr=${$1:0:7}
How do I find out from which repository is a package in CentOS?
$repoquery -i openssh
How do I revoke a certificate in Openssl?
#openssl -ca revoke openssl ca -revoke /etc/ssl/certs/cert.pem
Of course replace path and filename to reflect your configuration.
How do I find to which Debian package a file belongs to?
$dpkg -S /path/to/file
How to prevent changing SELinux policy?
#setsebool secure_mode_policyload on
After that the SELinux policy (enforced or permissive) can be changed only after rebooting
How do I troublshoot the CIFS client in Linux?
Please activate tracing and debugging of the module cifs.ko by running these commands as root
#echo 1 > /proc/fs/cifs/traceSMB
#echo 7 > /proc/fs/cifs/cifsFYI
Then run dmesg to check for info
How to add a VLAN ID to a network interface?
First check if the the kernel module 8021q is loaded with
$lsmod | grep 8021q
if it is not loaded, load the relative module with
#modprobe 8021q
Then either
vconfig add IF VLAN_ID
or
ip add link IF name IF.VLAN_ID type vlan id VLAN_ID
Where IF is the network card interface: eth0, eth1, ens33, etc.
And VLAN_ID is the ID of your VLAN
For example if the VLAN ID is 5 and the ethernet interface is eth1, you can either run
#vconfig add eth1 50
or
#ip add link eth1 name eth1.5 type vlan id 5
You must be root or have the appropriate root permissions.