RedHat RH302 - RHCE (Redhat Certified Engineer)

When user creates the file/directory, user owner will be user itself and group owner will be the primary group of the user.

There is one Special Permission SGID bit, when you set the SGID bit on directory,When users creates the file/directory automatically owner group will be same as a parent directory.

chmod g+s /data

Verify using: ls -ld /data

You will get: drwxrws---

By default user1 can remove user2’s files due to directory permission to group member. We can prevent of deleting files from others users using Sticky Bits.

chmod o+t /data

Verify /data: ls -ld /data

You will get: drwxrwx—T

Do the following steps as:

1.cat >schedule

*/2 * * * * /bin/echo “Hello World” >/dev/tty8

crontab schedule

Verify using: crontab –l

service crond restart

Cron helps to schedule on recurring events. Pattern of Cron is:

MinuteHourDay of MonthMonthDay of WeekCommands

0-590-231-311-120-7 where 0 and 7 means Sunday.

Note * means every. To execute the command on every two minutes */2.

To add the scheduled file on cron job: crontab filename

To List the Cron Shedule: crontab –l

To Edit the Schedule: crontab –e

To Remove the Schedule: crontab –r

Do the following steps as:

usermod -G training user1

usermod -G training user2

usermod -G training user3

Verify from : cat /etc/group

There are two types of group, I) primary group II) Secondary or supplementary group.

Primary Group: Primary group defines the files/directories and process owner group there can be only one primary group of one user.

Secondary Group is used for permission. Where permission are defined for group members, user can access by belonging to that group.

Here user1, user2 and user3 belong as supplementary to training group. So these users get the permission of group member.

Do the following steps as:

useradd username

passwd username

usermod -e “date”

example: usermod -e “12 Feb 2006” user4

Verify: chage –l user4

Do the following steps as:

1.Verify the File whether Shared or not ? : cat /etc/exports

2.Start the nfs service: service nfs start

3.Start the portmap service: service portmap start

4.Make automatically start the nfs service on next reboot: chkconfig nfs on

5.Make automatically start the portmap service on next reboot: chkconfig portmap on

6.Verify either sharing or not: showmount –e localhost

7.Check that default firewall is running on system ? if running flush the iptables using iptables –F and stop the iptables service.

#vi /etc/resolv.conf

nameserver 172.24.254.254

# dig server1.example.com

#host server1.example.com

DNS is the Domain Name System, which maintains a database that can help your computer translate domain names such as www.redhat.com to IP addresses such as 216.148.218.197. As no individual DNS server is large enough to keep a database for the entire Internet, they can refer requests to other DNS servers.

DNS is based on thenameddaemon, which is built on the BIND (Berkeley Internet Name Domain) package developed through the Internet Software Consortium

Users wants to access by name so DNS will interpret the name into ip address. You need to specify the Address if DNS server in each and every client machine. In Redhat Enterprise Linux, you need to specify the DNS server into /etc/resolv.conf file.

After Specifying the DNS server address, you can verify using host, dig and nslookup commands.

Do the following steps as:

1.First check the size of Logical Volume: lvdisplay /dev/vo/myvol

2.Make sure that the filesystem is in a consistent state before reducing:

# fsck –f /dev/vo/myvol

3.Now reduce the filesystem by 200MB.

# resize2fs /dev/vo/myvol 200M

4.It is now possible to reduce the logical volume.

#lvreduce /dev/vo/myvol –L 200M

4.Verify the Size of Logical Volume: lvdisplay /dev/vo/myvol

5.Verify that the size comes in online or not: df -h

Do the following steps as:

Use fdisk /dev/hdaTo create new partition.

Type nFor New partitions

It will ask for Logical or Primary Partitions. Press l for logical.

It will ask for the Starting Cylinder: Use the Default by pressing Enter Key.

Type the Size: +100MYou can Specify either Last cylinder of Size here.

Press P to verify the partitions lists and remember the partitions name.

Press w to write on partitions table.

Either Reboot or use partprobe command.

Use mkfs –t ext3 /dev/hda?

Or

mke2fs –j /dev/hda? To create ext3 filesystem.

vi /etc/fstab

Write:

/dev/hda?/dataext3defaults0 0

Verify by mounting on current Sessions also:

mount /dev/hda? /data

In Network problem thinks to check:

IP Configuration: use ifconfig command either IP is assigned to interface or not?

Default Gateway is set or not?

Hostname is set or not?

Routing problem is there?

Device Driver Module is loaded or not?

Device is activated or not?

Check In this way:

use ifconfig command and identify which IP is assigned or not.

cat /etc/sysconfig/networkWhat, What is written here. Actually here are these parameters.

NETWORKING=yes or no

GATEWAY=x.x.x.x

HOSTNAME=?

NISDOMAIN=?

Correct the file

Use vi /etc/sysconfig/network-scirpts/ifcfg-eth0 and check the proper options

DEVICE=eth0

ONBOOT=yes

BOOTPROTO=static

IPADDR=x.x.x.x

NETMAKS=x.x.x.x

GATEWAY=x.x.x.x

Use service network restart or start command