by George Sruthin | Jul 18, 2017 | Howtos, Linux, Mac, OS, Security
To give permission to execute a file you should navigate to file copied location in terminal
by default when you open-up the terminal your terminal location will look some thing like this
george@Area51-HP-Pro-3330-MT ~ $
if you type "pwd"
you can see current directory in the terminal
george@Area51-HP-Pro-3330-MT ~ $ pwd
/home/george <---- currently i have mounted to /home/user
for this tutorial i have copied file in a folder in the desktop so i have to navigate to that directory for eg: my folder name is called "Dashboard"
to navigate that folder i have to type in cd /Desktop/Dashboard
after that type ls so that you can list all files in the terminal
they type following command in the terminal , in my case i am using NVIDIA-Linux-x86_64-375.66.run file as executable this may vary with yours
sudo chmod +x ./NVIDIA-Linux-x86_64-375.66.run
* Note
sudo = root "super user " permission
chmod = The command name chmod stands for "change mode", and it is used to define the way a file can be accessed.
+x = this will execute a file
./ = if you are using a script .sh or .run you should use this following by the file name
if you use -x instead of +x this will remove file permission
sudo chmod -x ./NVIDIA-Linux-x86_64-375.66.run
This is will remove permissions
by Teffin Varghese | Jul 8, 2017 | Howtos, Linux, Networking, OS, Security, Storages, Troubleshooting
A Distributed Denial-of-Service (DDoS) attack is an attack in which multiple compromised computer systems attack a target, such as a server, website or other network resource, and cause a denial of service for users of the targeted resource. The flood of incoming messages, connection requests or malformed packets to the target system forces it to slow down or even crash and shut down, thereby denying service to legitimate users or systems.
How DDoS Attacks Work
In a DDoS attack, the incoming traffic flooding the victim originates from many different sources – potentially hundreds of thousands or more. This effectively makes it impossible to stop the attack simply by blocking a single IP address; plus, it is very difficult to distinguish legitimate user traffic from attack traffic when spread across so many points of origin.
Types of DDoS Attacks
There are many types of DDoS attacks. Common attacks include the following:
Traffic attacks: Traffic flooding attacks send a huge volume of TCP, UDP and ICPM packets to the target. Legitimate requests get lost and these attacks may be accompanied by malware exploitation.
Bandwidth attacks: This DDos attack overloads the target with massive amounts of junk data. This results in a loss of network bandwidth and equipment resources and can lead to a complete denial of service.
Application attacks: Application-layer data messages can deplete resources in the application layer, leaving the target’s system services unavailable.
For Linux Servers
1. Find to which IP address in the server is targeted by the DDoS attack
#netstat -plan | grep :80 | awk ‘{print $4}’ | cut -d: -f1 |sort |uniq -c
2. To find from which IPs, the attack is coming
#netstat -plan | grep :80 | awk ‘{print $5}’ | cut -d: -f1 |sort |uniq -c
3. For securing the server against DDoS/Drop Sync Attack
In /etc/sysctl.conf
Paste the following into the file, you can overwrite the current information.
#Kernel sysctl configuration file for Red Hat Linux
# For binary values, 0 is disabled, 1 is enabled. See sysctl(8) and
# sysctl.conf(5) for more details.
# Disables packet forwarding
net.ipv4.ip_forward=0
# Disables IP source routing
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.lo.accept_source_route = 0
net.ipv4.conf.eth0.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
# Enable IP spoofing protection, turn on source route verification
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 1
net.ipv4.conf.eth0.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
# Disable ICMP Redirect Acceptance
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.lo.accept_redirects = 0
net.ipv4.conf.eth0.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
# Enable Log Spoofed Packets, Source Routed Packets, Redirect Packets
net.ipv4.conf.all.log_martians = 0
net.ipv4.conf.lo.log_martians = 0
net.ipv4.conf.eth0.log_martians = 0
# Disables IP source routing
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.lo.accept_source_route = 0
net.ipv4.conf.eth0.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
# Enable IP spoofing protection, turn on source route verification
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 1
net.ipv4.conf.eth0.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
# Disable ICMP Redirect Acceptance
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.lo.accept_redirects = 0
net.ipv4.conf.eth0.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
# Disables the magic-sysrq key
kernel.sysrq = 0
# Decrease the time default value for tcp_fin_timeout connection
net.ipv4.tcp_fin_timeout = 15
# Decrease the time default value for tcp_keepalive_time connection
net.ipv4.tcp_keepalive_time = 1800
# Turn off the tcp_window_scaling
net.ipv4.tcp_window_scaling = 0
# Turn off the tcp_sack
net.ipv4.tcp_sack = 0
# Turn off the tcp_timestamps
net.ipv4.tcp_timestamps = 0
# Enable TCP SYN Cookie Protection
net.ipv4.tcp_syncookies = 1
# Enable ignoring broadcasts request
net.ipv4.icmp_echo_ignore_broadcasts = 1
# Enable bad error message Protection
net.ipv4.icmp_ignore_bogus_error_responses = 1
# Log Spoofed Packets, Source Routed Packets, Redirect Packets
net.ipv4.conf.all.log_martians = 1
# Increases the size of the socket queue (effectively, q0).
net.ipv4.tcp_max_syn_backlog = 1024
# Increase the tcp-time-wait buckets pool size
net.ipv4.tcp_max_tw_buckets = 1440000
# Allowed local port range
net.ipv4.ip_local_port_range = 16384 65536
Run /sbin/sysctl -p and sysctl -w net.ipv4.route.flush=1 to enable the changes without a reboot.
TCP Syncookies
echo 1 > /proc/sys/net/ipv4/tcp_syncookies
Some IPTABLES Rules:
iptables -A INPUT -p tcp –syn -m limit –limit 1/s –limit-burst 3 -j RETURN
iptables -A INPUT -p tcp –syn -m state –state ESTABLISHED,RELATED –dport 80 -m limit –limit 1/s –limit-burst 2 -j ACCEPT
by Teffin Varghese | Jun 10, 2017 | Howtos, Linux, Networking, OS, Servers, Storages, Troubleshooting
Distributed Replicated Block Device (DRBD)
DRBD is a distributed replicated storage system for the Linux platform. It is implemented as a kernel driver, several user space management applications, and some shell scripts. DRBD is traditionally used in high availability (HA) computer clusters, but beginning with DRBD version 9, it can also be used to create larger software defined storage pools with a focus on cloud integration.
Comparison to RAID-1
=====================
DRBD bears a superficial similarity to RAID-1 in that it involves a copy of data on two storage devices, such that if one fails, the data on the other can be used. However, it operates in a very different way from RAID and even network RAID.
In RAID, the redundancy exists in a layer transparent to the storage-using application. While there are two storage devices, there is only one instance of the application and the application is not aware of multiple copies. When the application reads, the RAID layer chooses the storage device to read. When a storage device fails, the RAID layer chooses to read the other, without the application instance knowing of the failure.
In contrast, with DRBD there are two instances of the application, and each can read only from one of the two storage devices. Should one storage device fail, the application instance tied to that device can no longer read the data. Consequently, in that case that application instance shuts down and the other application instance, tied to the surviving copy of the data, takes over.
Conversely, in RAID, if the single application instance fails, the information on the two storage devices is effectively unusable, but in DRBD, the other application instance can take over.
How it Works
============
The tool is built to imperceptibly facilitate communication between two servers by minimizing the amount of system resources used- It therefore does not affect system performance and stability.
DRBD facilitates communication by mirroring two separate servers- one server, although passive, is usually a direct copy of the other. Any data written to the primary server is simultaneously copied to the secondary one through a real time communication system. Any change made on the data is also immediately replicated by the passive server.
The passive server only becomes active when the primary one fails and collapses. When such a failure occurs, DRBD immediately recognizes the mishap and shifts to the secondary server. This shifting process however, is optional- it can either be manual or automatic. For users who prefer manual, one is required to authorize the system to shift to the passive server when the primary one fails. Automatic systems on the other hand, swiftly recognize problems within the primary servers and immediately shift to the secondary ones.
DRBD installation
=================
Install ELRepo repository on your both system:
———————————————-
# rpm -Uvh http://www.elrepo.org/elrepo-release-6-6.el6.elrepo.noarch.rpm
Update both repo
————————
yum update -y
setenforce 0
Install DRBD
—————–
[root@server1 ~]# yum -y install drbd83-utils kmod-drbd83
[root@server1 ~]# yum -y install drbd83-utils kmod-drbd83
Insert DRBD module manually on both machines or reboot
———————————————————————————
/sbin/modprobe drbd
Partition DRBD on both machines
———————————————-
[root@server1 ~]# fdisk -cu /dev/sdb
[root@server2 ~]# fdisk -cu /dev/sdb
Create the Distributed Replicated Block Device resource file
————————————————————————————-
[root@server1 ~]# vi /etc/drbd.d/clusterdb.res
resource clusterdb
{
startup {
wfc-timeout 30;
outdated-wfc-timeout 20;
degr-wfc-timeout 30;
}
net {
cram-hmac-alg sha1;
shared-secret sync_disk;
}
syncer {
rate 10M;
al-extents 257;
on-no-data-accessible io-error;
}
on server1 {
device /dev/drbd0;
disk /dev/sdb1;
address 192.165.1.111:7788;
flexible-meta-disk internal;
}
on server2 {
device /dev/drbd0;
disk /dev/sdb1;
address 192.165.1.111:7788;
meta-disk internal;
}
}
Make sure that DNS resolution is working
———————————————————-
/etc/hosts
192.168.1.110 server1 server1.example.com
192.168.1.111 server2 server2.example.com
Set NTP server and add it to crontab on both machines
—————————————————————————–
vi /etc/crontab
5 * * * * root ntpdate your.ntp.server
Copy DRBD configured and hosts file to server2
——————————————————————-
[root@server1 ~]# scp /etc/drbd.d/clusterdb.res server2:/etc/drbd.d/clusterdb.res
[root@server1 ~]# scp /etc/hosts server2:/etc/
Initialize the DRBD meta data storage on both machines
—————————————————————————–
[root@server1 ~]# drbdadm create-md clusterdb
[root@server2 ~]# drbdadm create-md clusterdb
Start the drdb on both servers
——————————————–
[root@server1 ~]# service drbd start
[root@server2 ~]# service drbd start
On the PRIMARY server run drbdadm command
——————————————————————
[root@server1 ~]# drbdadm — –overwrite-data-of-peer primary all
Check if Device disk initial synchronization to complete (100%) and check to confirm you are on primary server
———————————————————————————————————————————————————–
[root@server1 yum.repos.d]# cat /proc/drbd
version: 8.3.16 (api:88/proto:86-97)
GIT-hash: a798fa7e274428a357657fb52f0ecf40192c1985 build by phil@Build32R6, 2013-09-27 15:59:12
0: cs:SyncSource ro:Primary/Secondary ds:UpToDate/Inconsistent C r—–
ns:78848 nr:0 dw:0 dr:79520 al:0 bm:4 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:2017180
[>………………..] sync’ed: 27.0% (2037180/2096028)K
finish: 0:02:58 speed: 11,264 (11,264) K/sec
ns:1081628 nr:0 dw:33260 dr:1048752 al:14 bm:64 lo:0 pe:0 ua:0 ap:0 ep:1 wo:f oos:0]
Create filesystem on Distributed Replicated Block Device device
——————————————————————————————-
[root@server1 yum.repos.d]# /sbin/mkfs.ext4 /dev/drbd0
mke2fs 1.41.12 (06-June-2017)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
131072 inodes, 524007 blocks
26200 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=536870912
16 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912
Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 26 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
Now you can mount DRBD device on your primary server
————————————————–
[root@server1 ~]# mkdir /data
[root@server1 ~]# mount /dev/drbd0 /data
You don’t need to mount the disk from secondary machines. All data you write on /data folder will be synced to machine2.
Adios 🙂
by Teffin Varghese | Jun 5, 2017 | Howtos, Linux, OS, Servers, Storages, Troubleshooting
Okay, What is RAID 🙂
RAID (Redundant Array of Independent Disks) is a data storage virtualization technology.
It combines multiple inexpensive,small disk drives into an array of disks in order to
provide redundancy, lower latency and maximized the chance to recover data from the hard drives
If they crashes. And there by improving the performance.
The RAID appears to the system as a single drive.
RAID can be implemented via Hardware devices as RAID controllers or via software
controlled by the Linux Kernel.
The most commonly used RAID levels are
RAID 0 [Minimum of 2 Disk]
RAID 1 [Minimum of 2 Disk]
RAID 5 [Minimum of 3 Disk]
RAID 10 [Minimum of 4 Disk]
==============================================
RAID 1
RAID 1 is also known as “disk
mirroring.” With RAID 1, data is copied seamlessly and simultaneously from one drive to another, creating an exact copy or mirror.
If one of the disk on raid array fails, the other can work without issues. It’s the simplest way to implement fault tolerance storage. But it slightly drag the performance.
This is useful when read performance or reliability is more important than the resulting data storage capacity.
The advantages of raid 1 are it offers excellent read speed and a write-speed that is comparable to that of a single drive and if a drive fails, data do not have to be rebuild, they just need to be copied to a new replacement drive.
The main disadvantage of RAID 1 is that the effective storage capacity is only half of the total drive capacity
because all data get written twice and software RAID 1 solutions do not always allow a hot swap of a failed drive.
Configuring RAID level 1 using mdadm.
Install mdadm on your server.
You can use the following commands to installmdadm.
For RHEL/CentOS/Fedora:
=======================
# yum install mdadm
And for Debian/Ubuntu:
=======================
#apt-get update
#apt-get install mdadm
The next step is to create a RAID array. For that create the disk partitions (with the same size) that are going to be the array members as RAID partition.
To create partitions you can use the following commands.
#fdisk -l | grep /dev/sd (This command will list the disks on the server.eg: the disks on the server are sdb & sdc)
Then choose one disk eg: sdb
#fdisk /dev/sdb
Then press ‘n’ for creating a new partition in /dev/sdb. Then press ‘p’ for use it as primary partition.
Enter the partition number. You can use the full size by just pressing two times ‘Enter key’.
Then press ‘t’ to choose the partition type. Then choose ‘fd‘ for Linux raid auto and press ‘Enter Key’ to apply it.
Pressing ‘p’ verify that the partition is created as Linux raid auto detect.
Press ‘w’ to save the changes.
Follow the same instructions to create new partition on /dev/sdc drive with the same partition size.
The next step is to create a RAID 1 sdb1,sdc1 array using command mdadm:
# mdadm –create –verbose –level=1 –raid-devices=2 /dev/md0 /dev/sdb1 /dev/sdc1
xxxxxxxxxx
–create–> create a new RAID device.
–verbose–>print information about its operations.
/dev/md0 is the new RAID device that we want to create.
–level–> defines the RAID level; in our case, RAID 1.
–raid-devices –> It specifies how many disks (devices) are going to be used in the creation of the new RAID device.(here 2 — /dev/sdb1 /dev/sdc1)
xxxxxxxxx
You can verify raid status using the following command.
#cat /proc/mdstat
#mdadm -E /dev/sd[b-c]1
# mdadm –detail /dev/md0
The next step is formatting the partition and creating a file system and mount the partition.
#mkfs.ext4 /dev/md0 –> to format the partition
To mount /dev/md0 to /raid1 perform the below steps.
# mkdir /raid1
# mount /dev/md0 /raid1
# df -H –> you can verify it is mounted or not.
To auto-mount RAID1 on system reboot, need to make an entry in ‘/etc/fstab‘ file.
For that add the following line to the fstab.
/dev/md0 /raid1 ext4 defaults 0 0
Then run ‘mount -a‘ to check whether there are any errors on fstab entry.
Now update /etc/mdadm/mdadm.conf or/etc/mdadm.conf file as follows:
ARRAY /dev/md0 devices=/dev/sdb1,/dev/sdc1 level=1num-devices=2 auto=yes
or
# mdadm –detail –scan >> /etc/mdadm.conf
That’s all for now. 🙂
by George Sruthin | Jun 1, 2017 | Howtos, Networking, OS, Windows
- In Server Manager, click Local Server.
- In the Properties pane locate NIC Teaming, and then click the link Disabled to the right. The NIC Teaming dialog box opens.
- In Adapters and Interfaces, select the network adapters that you want to add to a NIC Team.
- Click TASKS or Right Click, and then click Add to New Team.
- The New team dialog box opens and displays network adapters and team members. In Team name, type a name for the new NIC Team.you can get an option to select interface then click okay
- after that go and check your network adapters , now you can see a new adapter with Nic team name, change ip in that adapter, done
enjoy
by George Sruthin | Jun 1, 2017 | Howtos, Troubleshooting, Windows
Today when i install Windows Server 2012 r2 OS in a new HPE Proliant DL 380 server, after the os installation i have added ip manually to the Ethernet interface, but i get a Limited Access error,so i double check the ip is correct or not, i was right ip is correct, so i disabled firewall ,then i checked by typing ipconfig in the command prompt and i get result as follows
Ethernet adapter Ethernet:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : HP Ethernet 1Gb 4-port 331T Adapter
Physical Address. . . . . . . . . : 3C-A8-2A-F3-CF-9C
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::f0e1:58c8:4e40:4513%12(Preferred)
IPv4 Address. . . . . . . . . . . : 10.60.148.43(Duplicate)
Subnet Mask . . . . . . . . . . . : 255.255.255.224
Autoconfiguration IPv4 Address. . : 169.254.69.19(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.0.0
Default Gateway . . . . . . . . . : 10.60.148.33
DNS Servers . . . . . . . . . . . : 10.60.148.36
10.1.12.43
NetBIOS over Tcpip. . . . . . . . : Enabled
as you can see there is two ipv4 ip's , one is the ip which i given , second is APIPA range ip
to fix this please follow the steps
- Click on start and click on RUN (or simple press windowsKey+R ) type CMD
- type ipconfig
this is will give you following result
Ethernet adapter Ethernet:
Connection-specific DNS Suffix . :
Description . . . . . . . . . . . : HP Ethernet 1Gb 4-port 331T Adapter
Physical Address. . . . . . . . . : 3C-A8-2A-F3-CF-9C
DHCP Enabled. . . . . . . . . . . : No
Autoconfiguration Enabled . . . . : Yes
Link-local IPv6 Address . . . . . : fe80::f0e1:58c8:4e40:4513%12(Preferred)
IPv4 Address. . . . . . . . . . . : 10.60.148.43(Duplicate)
Subnet Mask . . . . . . . . . . . : 255.255.255.224
Autoconfiguration IPv4 Address. . : 169.254.69.19(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.0.0
Default Gateway . . . . . . . . . : 10.60.148.33
DNS Servers . . . . . . . . . . . : 10.60.148.36
10.1.12.43
NetBIOS over Tcpip. . . . . . . . : Enabled
now type below code in the command prompt
netsh interface ipv4 show inter
this will show you below resurlt
C:\\Users\\Administrator>netsh interface ipv4 show inter
Idx Met MTU State Name
--- ---------- ---------- ------------ ---------------------------
1 50 4294967295 connected Loopback Pseudo-Interface 1
12 10 1500 connected Ethernet
13 5 1500 disconnected Embedded LOM 1 Port 1
14 5 1500 disconnected Ethernet 2
15 5 1500 disconnected Embedded LOM 1 Port 2
16 5 1500 disconnected Ethernet 3
17 5 1500 disconnected Ethernet 4
18 5 1500 disconnected Embedded LOM 1 Port 3
19 5 1500 disconnected Embedded LOM 1 Port 4
check for the connected interface
from the above command result you can find the connected interface notedown its idx id which is 12 in my case but your id may vary , type following command with your idx id in the command prompt then press enter
netsh interface ipv4 set interface 12 dadtransmits=0 store=persistent
this will give you following result
C:\\Users\\Administrator>netsh interface ipv4 set interface 12 dadtransmits=0 store=persistent
Ok.
- Click on start and click on RUN (or simple press windowsKey+R ) type CMD and Type Services.msc a box will appear Search for DHCP client right click on it and Click on Properties click on Startup Type select Disable
- Now Click on Stop Button Below And click on Ok
* Note
- Unplug Your Lan Cable And Restart your System
- After Restart don't Plugin your Cable, Come again to Services.msc find DHCP client right click on it and Click on Properties click on Startup Type now select Automatic
- Click on Start button below and then Ok.
- Now Plugin your Lan Cable and Enjoy.
