Troubleshooting of Linux Issues Part - 3

How to set password to grup.conf file

#grub   ----enter

#grub> md5crypt   ----------password level

#password : **   (xx – set password )

#Encrypted : $1LQzsdasdafkafjkawyfaerfndjsfnsfjoisrhgsrh43  -----encrypted password copy

#grub>quit

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#go to the /etc/grup.conf and add password above title

Example

#vi /etc/grub.conf

#boot=/dev/sda

default=0 

timeout=5  

splashimage=(hd0,0)/grub/kcm-grub2-0.6.4.tar.gz 

hiddenmenu

password –md5 $1LQzsdasdafkafjkawyfaerfndjsfnsfjoisrhgsrh43     ---- paste  password

title CentOS (2.6.32-431.el6.x86_64) 

root (hd0,4)   (hd0 -----HDD) 

kernel /vmlinuz-2.6.32-431.el6.x86_64 ro root=UUID=c79924a2-5e11-440d-add6-522144dec58d rd_NO_LUKS rd_NO_LVM LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto  KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM rhgb quiet  

initrd /initramfs-2.6.32-431.el6.x86_64.img

wq!

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After above steps reboot the system and try to edit grub file white booting

When you try edit on kernel or grab file you get prompt for password
press p:

Password: xx -----entry (you can edit the grub file )
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We can set grub password before login& paste password below title line

#go to the /etc/grup.conf and add password below the title

Example

#vi /etc/grub.conf

#boot=/dev/sda

default=0 

timeout=5  

splashimage=(hd0,0)/grub/kcm-grub2-0.6.4.tar.gz 

hiddenmenu

title CentOS (2.6.32-431.el6.x86_64) 

password –md5 $1LQzsdasdafkafjkawyfaerfndjsfnsfjoisrhgsrh43     ---- paste  password

root (hd0,4)   (hd0 -----HDD) 

kernel /vmlinuz-2.6.32-431.el6.x86_64 ro root=UUID=c79924a2-5e11-440d-add6-

522144dec58d rd_NO_LUKS rd_NO_LVM LANG=en_US.UTF-8 rd_NO_MD

SYSFONT=latarcyrheb-sun16 crashkernel=auto  KEYBOARDTYPE=pc KEYTABLE=us

rd_NO_DM rhgb quiet  

initrd /initramfs-2.6.32-431.el6.x86_64.img

wq!

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Above entry we can’t boot without grub password

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HOW TO BLOCK DRIVERS AND USB STORAGE

 We have 2 ways to block usb storage or drivers

1)   go to grup.conf

2)   modprobe.d/blacklist.conf

#vi /etc/grub.conf

Example

#vi /etc/grub.conf

#boot=/dev/sda

default=0 

timeout=5  

splashimage=(hd0,0)/grub/kcm-grub2-0.6.4.tar.gz 

hiddenmenu

title CentOS (2.6.32-431.el6.x86_64) 

root (hd0,4)   (hd0 -----HDD) 

kernel /vmlinuz-2.6.32-431.el6.x86_64 ro root=UUID=c79924a2-5e11-440d-add6-

522144dec58d rd_NO_LUKS rd_NO_LVM LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto  KEYBOARDTYPE=pc KEYTABLE=us nousbrd_NO_DM rhgb quiet  

initrd /initramfs-2.6.32-431.el6.x86_64.img

wq!

Reboot the system and check, because after reboot this file execute

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Check usb storage drive connected status

# lsmod | grep usb_storage

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#modprobe –r usb_storage  ------temporary

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#vi /etc/modprobe.d/blacklist.conf    ----permanent

blacklist usb_storage

wq!
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HOW TO RESET LINUX ROOT PASSOWRD 

Go to splash window and press a

Press space and 1 enter

grup append> ro root=LABEL=/ hdc=ide=scsi 1

We get shell prompt

#passwd root   ---change root password

#qwerty    ------set root password

Reboot and try new password

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How to change Linux date & time

# date -s "2 OCT 2006 18:00:00"  -  set new data to  2 Oct 2006 18:00:00,

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Windows vs Linux -----3 different

Linux vs Unix       -----3 different

Linux is free                    ----- Unix is proprietors ( commercial)

Hardware independent    ----- Hardware dependent

Linux has source code     ----  Unix no source code

 Xser ---for Linux           -----  Unix  ( HP  UX  --- IBM   AIX )

                                        ------  IBM  ---X-Serve’s

                                        ------  IBM  ---P-Serve’s

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How to delete history permanently

# history –c  ------------------clear temporary

#  > /root/.bash_history   ------- clear permanent

#  >   ------- means empty file

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Server vs desktop

Symlinks vs Hardlinks

Archive vs compression

Telnet VS ssh

# Telnet – telnet transfer the ip packet in clear text mode

# ssh – Secure socket host

            ssh is transfer the ip packet in encryption  mode

            [ Public license key + Private key ]

Request
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how to secure single user mode - Password Protect Single User Mode in Red Hat or CentOS

Allowing access to single user mode in Linux is a major security risk. Setting it to require the root password before booting into single user mode is a good idea.

[root@localhost tushar]# vi /etc/inittab

# password protect single user mode

su:S:wait:/sbin/sulogin

#

How to require password for single user mode in CentOS 5 / RedHat 5:
Insert the following line to /etc/inittab file above the line containing initdefault.

su:S:wait:/sbin/sulogin

NOTE: it must be above the link with initdefault in order to work. Example:
# Password requires for single user mode.
su:S:wait:/sbin/sulogin
# Default runlevel. The runlevels used by RHS are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
#
id:3:initdefault:

How to require password for single user mode in CentOS 6 / RedHat 6:
Edit the file /etc/sysconfig/init and change the following line:
SINGLE=/sbin/sushell
to
SINGLE=/sbin/sulogin

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