Linux

From coopzone
Jump to navigation Jump to search

Debian locale settings incorrect

run dpkg-reconfigure tzdata

and

dpkg-reconfigure locales

Setting the timezone manually

  • Change to the directory /usr/share/zoneinfo here you will find a list of time zone regions. Choose the most appropriate region, if you live in Canada or the US this directory is the "America" directory. UK time zones are under Europe etc.
  • Backup the previous timezone. mv /etc/localtime /etc/localtime-old
  • Create a symbolic link to the appropriate timezone from /etc/localtime. Example:
ln -sf /usr/share/zoneinfo/Europe/Amsterdam /etc/localtime
  • If you have the utility rdate, update the current system time by executing
/usr/bin/rdate -s time-a.nist.gov
  • Set the ZONE entry in the file /etc/sysconfig/clock file (e.g. "Europe/London")

Grub Notes

To re-install grub manually (mostly for raid systems, if you want more than one drive to be bootable) 

grub
grub> device (hd0) /dev/sda
grub> root (hd0,0)
grub> setup (hd0)

grub> setup (hd0)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/e2fs_stage1_5" exists... yes
 Running "embed /boot/grub/e2fs_stage1_5 (hd0)"...  15 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd0) (hd0)1+15 p (hd0,0)/boot/grub/stage2 /boot/grub/menu.lst"... succeeded
Done.

grub> quit

Repeat above for each drive. Note the (hd0,0) refers to the boot partion.

mdadm

Example: To replace a drive

Fail the drive you want to replace in the array, i.e.

mdadm --manage /dev/mdx --fail /dev/hdxy

shutdown the system, replace the drive.

If the drive is not already blank, you may need to remove any previous raid usage:

boot from cd, rescue mode.

For most commands to work you need an /etc/mdadm.conf.

This can be setup using "mdadm -E --scan >/etc/mdadm.conf"

To get the /etc/mdadm.conf file from the drives in the system.

madam --zero-superblock /dev/hdxy for each partionion.

remove the partitions, recreate from an existing drive

sfdisk -d /dev/hdx | sfdiisk /dev/hdy


start the array used by the root filesystem

madam -A /dev/md1 --force --run

add the new drive/partion to the root md device

madam --manage /dev/md1 --add /dev/hdxy

wait for rebuild

do the same for the /boot patron

finally any data partions you have, these can be done either from a rescue setup or after a reboot.

Growing encrypted disks

This example show a domU client, since the disk is allocated in the Dom0 using lvm, you need to grow that first! 

[root@skype ~]# mkdir /data
[root@skype ~]# mount /dev/mapper/data /data
[root@skype ~]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/xvda              2064208   1499312    460040  77% /
tmpfs                    98396         0     98396   0% /dev/shm
/dev/mapper/data      77403712    184220  73287612   1% /data

fdisk -l (to find the correct partion layout/names etc)

Disk /dev/xvdb: 268 MB, 268435456 bytes
255 heads, 63 sectors/track, 32 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System
/dev/xvdb1               1          32      257008+  82  Linux swap / Solaris

Disk /dev/xvdc: 107.3 GB, 107374182400 bytes
255 heads, 63 sectors/track, 13054 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System
/dev/xvdc1               1        9790    78638143+  83  Linux

Use fdisk to remove and re add a partition to grow the disk into 

[root@skype ~]# fdisk /dev/xvdc

The number of cylinders for this disk is set to 13054.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Command (m for help): p

Disk /dev/xvdc: 107.3 GB, 107374182400 bytes
255 heads, 63 sectors/track, 13054 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System
/dev/xvdc1               1        9790    78638143+  83  Linux

Delete and re add partition 

Command (m for help): d
Selected partition 1

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-13054, default 1): 
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-13054, default 13054): 
Using default value 13054

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

Re Open the Luks Device 

[root@skype ~]# cryptsetup luksOpen /dev/xvdc1 data
Enter LUKS passphrase for /dev/xvdc1: 
padlock: VIA PadLock not detected.
key slot 0 unlocked.
Command successful.

Make sure crypto is aware of the new size 

[root@skype ~]# cryptsetup resize data

Then resize it 

[root@skype ~]# fsck.ext3 -f /dev/mapper/data 
e2fsck 1.39 (29-May-2006)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/data: 30743/9830400 files (0.1% non-contiguous), 546498/19659406 blocks

[root@skype ~]# resize2fs /dev/mapper/data 
resize2fs 1.39 (29-May-2006)
Resizing the filesystem on /dev/mapper/data to 26213926 (4k) blocks.
The filesystem on /dev/mapper/data is now 26213926 blocks long.

And re-mount it ready for use 

[root@skype ~]# mount /dev/mapper/data /data

[root@skype ~]# df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/xvda              2064208   1499392    459960  77% /
tmpfs                    98396         0     98396   0% /dev/shm
/dev/mapper/data     103210424    960112  97007532   1% /data

ISCSI redhat connect to target

First you need to discover targets under portal IP address: 

iscsiadm --mode discovery --type sendtargets --portal 192.168.1.10 # Replace 192.168.1.10 with Your portal IP address

Login, must use a node record id found by the discovery: 

iscsiadm --mode node --targetname iqn.2001-05.com.doe:test --portal 192.168.1.1:3260 --login

Logout: 

iscsiadm --mode node --targetname iqn.2001-05.com.doe:test --portal 192.168.1.1:3260 --logout

Display info about target: 

iscsiadm -m node -T targetname -p ipaddress

List node records: 

iscsiadm --mode node

Display list of all current sessions logged in 

iscsiadm -m session

View iSCSI database regarding discovery 

iscsiadm -m discovery -o show

Display all data for a given node record: 

iscsiadm --mode node --targetname iqn.2001-05.com.doe:test --portal 192.168.1.1:3260

Pacemaker / Corosync notes

First, install all needed packages for pacemaker: 

 yum install heartbeat corosync pacemaker

Start service and make it bootable during the system startup: 

/etc/init.d/corosync start

After installation generate corosync key for nodes: 

corosync-keygen

Copy corosync key to second node: 

scp /etc/corosync/authkey 192.168.0.2:/etc/corosync/authkey

create /etc/corosync/service.d/pcmk on nodes with content : 

service {
        name: pacemaker
        ver:  0
}

Edit configuration files on both nodes: 

mv /etc/corosync/corosync.conf.example /etc/corosync/corosync.conf

Set bindnetaddr to network address others directives can be left without the changes: 

bindnetaddr: 192.168.0.0

Now configure Virtual IP resource for this nodes. Nodes have to check each other every 20 seconds: 

crm configure primitive P_IP ocf:heartbeat:IPaddr2 \
       params ip="192.168.0.3" cidr_netmask="255.255.255.0" \
       op monitor interval="20s"

And go up to next level. Httpd server resource: 

crm configure primitive P_APACHE ocf:heartbeat:apache \
       params configfile="/etc/httpd/conf/httpd.conf" statusurl="http://localhost/server-status" \
       op monitor interval="40s"

where

P_APACHE – resource name

configfile – path to apache configuration file

statusurl – url to status page( below how to configures one)

interval – time between checks

To prevent situation when resource apache migrate to node002 and resource IP stays at node001(It happens when apache at node001 hung but network stack works well) we need to make colocation 

crm configure colocation WEB_SITE inf: P_APACHE P_IP

To make pacemaker start up apache only after IP is set up. In other words describe start up order run: 

crm configure order START_ORDER inf: P_IP P_APACHE

Describe location priority:

location L_IP_NODE001 P_IP 100: node001.example.com

location L_IP_NODE002 P_IP 100: node002.example.com

Now set priority threshold. Value 110 is enough to prevent resource migration back. It could be happens when next scenario occurs:

1. node001 fails and resources are moved to node002.

2. then node001 is going online

3. resources are migrated to node001


To stick resources to node002 and prevent from further migration add resource-stickiness: 

crm configure rsc_defaults resource-stickiness="110"

# crm configure show
node node001.example.com
node node002.example.com
primitive P_APACHE ocf:heartbeat:apache \
        params configfile="/etc/httpd/conf/httpd.conf" statusurl="http://localhost/server-status" \
        op monitor interval="40s"
primitive P_IP ocf:heartbeat:IPaddr2 \
        params ip="10.22.48.138" cidr_netmask="255.255.255.240" \
        op monitor interval="20s"
colocation WEB_SITE inf: P_APACHE P_IP
order START_ORDER inf: P_IP P_APACHE
property $id="cib-bootstrap-options" \
        dc-version="1.0.10-da7075976b5ff0bee71074385f8fd02f296ec8a3" \
        cluster-infrastructure="openais" \
        expected-quorum-votes="2" \
        stonith-enabled="false" \
        no-quorum-policy="ignore"

Keep in mind that server-status page should be described at apache configuration files on both nodes as next: 

<VirtualHost 127.0.0.1:80>
    ServerAdmin webmaster@dummy-host.example.com
    ServerName localhost
    ErrorLog logs/dummy-host.example.com-error_log
    CustomLog logs/dummy-host.example.com-access_log common
    <Location /server-status>
        SetHandler server-status
        Order deny,allow
        Deny from all
        Allow from 127.0.0.1
    </Location>
</VirtualHost>

Finally check you pacemaker status: 

crm_mon
============
Last updated: Wed Jul  6 15:17:46 2011
Stack: openais
Current DC: node001.example.com - partition with quorum
Version: 1.0.10-da7075976b5ff0bee71074385f8fd02f296ec8a3
2 Nodes configured, 2 expected votes
2 Resources configured.
============
 
Online: [ node001.example.com node001.example.com ]
 
P_APACHE        (ocf::heartbeat:apache):        Started node001.example.com
P_IP        (ocf::heartbeat:IPaddr2):       Started node001.example.com

That means that two resources started at node001 where node002 in stand-by mode.

There are couples ways to move resources to other node:

1. Set active node to standby: 

crm node standby node001.example.com

2. Or directly move resource 

crm resource [resource_name] [node_name]

DRBD recover split brain

On the victim (may return error if already disconnected, ignore it): 

drbdadm disconnect <resource>
drbdadm secondary <resource>
drbdadm connect --discard-my-data <resource>

ON older 8.3 version use:
drbdadm -- --discard-my-data connect <resource>

On the other node (the split brain survivor), if its connection state is also StandAlone, you would enter: 

drbdadm connect <resource>

LVM

This is one of the benefits of LVM. Once you start seeing errors on a disk, it is high time to move your data. With LVM this is easy as pie. We first do the obvious replacement example where you add a disk to the system that's at least as large as the one you want to replace.

To move data, we move Physical Extents of a Volume Group to another disk, or more precisely, to another Physical Volume. For this, LVM offers us the pvmove utility.

Let's say that our suspicious disk is called /dev/hda1 and we want to replace it by /dev/sdb3. We first add /dev/sdb3 to the Volume Group that contains /dev/hda1.

It appears advisable to unmount any filesystems on this Volume Group before doing this. Having a full backup might not hurt either.

FIXME: is this necessary?

We then execute pvmove. In its simplest invocation, we just mention the disk we want to remove, like this: 

# pvmove /dev/hda1

pvmove -- moving physical extents in active volume group "test1" pvmove -- WARNING: moving of active logical volumes may cause data loss! pvmove -- do you want to continue? [y/n] y pvmove -- doing automatic backup of volume group "test1" pvmove -- 12 extents of physical volume "/dev/hda1" successfully moved Please heed this warning. Also, it appears that at least some kernels or LVM versions have trouble with this command. I tested it with 2.3.99pre6-2, and it works, but be warned.

Now that /dev/hda1 contains no Physical Extents anymore, we can reduce it from the Volume Group: 

# vgreduce test1 /dev/hda1

vgreduce -- doing automatic backup of volume group "test1" vgreduce -- volume group "test1" successfully reduced by physical volume: vgreduce -- /dev/hda1 FIXME: we need clarity on a few things. Should the volume group be active? When do we get data loss?

6.1 When it's too late

If a disk fails without warning and you are unable to move the Physical Extents off it to a different Physical Volume you will have lost data unless the Logical Volumes on the PV that failed was mirrored. The correct course of action is to replace the failed PV with an identical one or at least a partition of the same size.

The directory /etc/lvmconf contains backups of the LVM data and structures that make the disks into Physical Volumes and list which Volume Groups that PV belongs to and what Logical Volumes are in the Volume Group.

After replacing the faulty disk you can use the vgcfgrestore command to recover the LVM data to the new PV. This restores the Volume Group and all it's info, but it does not restore the data that was in the Logical Volumes. This is why most LVM commands make backups automatically of the LVM data when doing changes.

IPTABLES examples

# Modify this file accordingly for your specific requirement.
# http://www.thegeekstuff.com
# 1. Delete all existing rules
iptables -F

# 2. Set default chain policies
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP

# 3. Block a specific ip-address
#BLOCK_THIS_IP="x.x.x.x"
#iptables -A INPUT -s "$BLOCK_THIS_IP" -j DROP

# 4. Allow ALL incoming SSH
#iptables -A INPUT -i eth0 -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
#iptables -A OUTPUT -o eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

# 5. Allow incoming SSH only from a sepcific network
#iptables -A INPUT -i eth0 -p tcp -s 192.168.200.0/24 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
#iptables -A OUTPUT -o eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

# 6. Allow incoming HTTP
#iptables -A INPUT -i eth0 -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
#iptables -A OUTPUT -o eth0 -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT

# Allow incoming HTTPS
#iptables -A INPUT -i eth0 -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
#iptables -A OUTPUT -o eth0 -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

# 7. MultiPorts (Allow incoming SSH, HTTP, and HTTPS)
iptables -A INPUT -i eth0 -p tcp -m multiport --dports 22,80,443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp -m multiport --sports 22,80,443 -m state --state ESTABLISHED -j ACCEPT

# 8. Allow outgoing SSH
iptables -A OUTPUT -o eth0 -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

# 9. Allow outgoing SSH only to a specific network
#iptables -A OUTPUT -o eth0 -p tcp -d 192.168.101.0/24 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
#iptables -A INPUT -i eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

# 10. Allow outgoing HTTPS
iptables -A OUTPUT -o eth0 -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

# 11. Load balance incoming HTTPS traffic
#iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3 --packet 0 -j DNAT --to-destination 192.168.1.101:443
#iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3 --packet 1 -j DNAT --to-destination 192.168.1.102:443
#iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3 --packet 2 -j DNAT --to-destination 192.168.1.103:443

# 12. Ping from inside to outside
iptables -A OUTPUT -p icmp --icmp-type echo-request -j ACCEPT
iptables -A INPUT -p icmp --icmp-type echo-reply -j ACCEPT

# 13. Ping from outside to inside
iptables -A INPUT -p icmp --icmp-type echo-request -j ACCEPT
iptables -A OUTPUT -p icmp --icmp-type echo-reply -j ACCEPT

# 14. Allow loopback access
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

# 15. Allow packets from internal network to reach external network.
# if eth1 is connected to external network (internet)
# if eth0 is connected to internal network (192.168.1.x)
iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT

# 16. Allow outbound DNS
#iptables -A OUTPUT -p udp -o eth0 --dport 53 -j ACCEPT
#iptables -A INPUT -p udp -i eth0 --sport 53 -j ACCEPT

# 17. Allow NIS Connections
# rpcinfo -p | grep ypbind ; This port is 853 and 850
#iptables -A INPUT -p tcp --dport 111 -j ACCEPT
#iptables -A INPUT -p udp --dport 111 -j ACCEPT
#iptables -A INPUT -p tcp --dport 853 -j ACCEPT
#iptables -A INPUT -p udp --dport 853 -j ACCEPT
#iptables -A INPUT -p tcp --dport 850 -j ACCEPT
#iptables -A INPUT -p udp --dport 850 -j ACCEPT

# 18. Allow rsync from a specific network
iptables -A INPUT -i eth0 -p tcp -s 192.168.101.0/24 --dport 873 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 873 -m state --state ESTABLISHED -j ACCEPT

# 19. Allow MySQL connection only from a specific network
iptables -A INPUT -i eth0 -p tcp -s 192.168.200.0/24 --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 3306 -m state --state ESTABLISHED -j ACCEPT

# 20. Allow Sendmail or Postfix
iptables -A INPUT -i eth0 -p tcp --dport 25 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 25 -m state --state ESTABLISHED -j ACCEPT

# 21. Allow IMAP and IMAPS
iptables -A INPUT -i eth0 -p tcp --dport 143 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 143 -m state --state ESTABLISHED -j ACCEPT

iptables -A INPUT -i eth0 -p tcp --dport 993 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 993 -m state --state ESTABLISHED -j ACCEPT

# 22. Allow POP3 and POP3S
iptables -A INPUT -i eth0 -p tcp --dport 110 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 110 -m state --state ESTABLISHED -j ACCEPT

iptables -A INPUT -i eth0 -p tcp --dport 995 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 995 -m state --state ESTABLISHED -j ACCEPT

# 23. Prevent DoS attack
iptables -A INPUT -p tcp --dport 80 -m limit --limit 25/minute --limit-burst 100 -j ACCEPT

# 24. Port forwarding 422 to 22
iptables -t nat -A PREROUTING -p tcp -d 192.168.102.37 --dport 422 -j DNAT --to 192.168.102.37:22
iptables -A INPUT -i eth0 -p tcp --dport 422 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 422 -m state --state ESTABLISHED -j ACCEPT

# 25. Log dropped packets
iptables -N LOGGING
iptables -A INPUT -j LOGGING
iptables -A LOGGING -m limit --limit 2/min -j LOG --log-prefix "IPTables Packet Dropped: " --log-level 7
iptables -A LOGGING -j DROP
Retrieved from ‘http://wiki.coopzone.org.uk/mediawiki/index.php?title=Linux&oldid=233’