I will give a small list of some popular network protocols, the ports that they use and their brief description:Continue reading “List of network protocols and ports”
In this article I will give an example of generating keys and adding DKIM records.Continue reading “How to add DKIM record”
DMARC recors allow recipients and senders to verify the authenticity of messages, as well as determine what to do with messages that are not DKIM validated.Continue reading “How to add DMARC record”
You can buy a domain and hosting from a domain name registrar, for example godaddy.com
After the purchase you will need to configure the DNS settings in the control panel on the site where it is registered.Continue reading “How to buy and setup a domain”
I will give an example of adding MX records in the DNS settings of a domain name registrar.Continue reading “How to add MX record”
For example, take the server with the operating system Ubuntu Server 14.04, in which let’s say we changed the network settings when executing the commands:Continue reading “Why service networking restart or /etc/init.d/networking restart does not work”
In this article I will briefly describe the difference between MASQUERADE and SNAT.
MASQUERADE. Less fast routing than SNAT with mass requests, since for each new connection an IP address on the external network interface (WAN) is determined. Great for home use routers and when changing the IP address on the WAN interface.
Continue reading “Difference between MASQUERADE and SNAT”
In this article I’ll look at the SMART information of the first SSD drive that comes under the arm and describe what the attributes mean.
Suppose we looked at the information on the disk /dev/sda:
sudo smartctl -a /dev/sda
I have the following information:
ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 1 Raw_Read_Error_Rate 0x000b 100 100 050 Pre-fail Always - 0 2 Throughput_Performance 0x0005 100 100 050 Pre-fail Offline - 0 3 Spin_Up_Time 0x0007 100 100 050 Pre-fail Always - 0 5 Reallocated_Sector_Ct 0x0013 100 100 050 Pre-fail Always - 0 7 Unknown_SSD_Attribute 0x000b 100 100 050 Pre-fail Always - 0 8 Unknown_SSD_Attribute 0x0005 100 100 050 Pre-fail Offline - 0 9 Power_On_Hours 0x0012 100 100 000 Old_age Always - 2850 12 Power_Cycle_Count 0x0012 100 100 000 Old_age Always - 10 168 Unknown_Attribute 0x0012 100 100 000 Old_age Always - 0 170 Unknown_Attribute 0x0003 100 100 010 Pre-fail Always - 531 173 Unknown_Attribute 0x0012 100 100 000 Old_age Always - 12255496 175 Program_Fail_Count_Chip 0x0013 100 100 050 Pre-fail Always - 0 187 Reported_Uncorrect 0x0012 100 100 000 Old_age Always - 0 192 Power-Off_Retract_Count 0x0012 100 100 000 Old_age Always - 5 194 Temperature_Celsius 0x0023 071 067 030 Pre-fail Always - 29 (Min/Max 23/33) 196 Reallocated_Event_Count 0x0002 100 100 010 Old_age Always - 0 197 Current_Pending_Sector 0x0032 100 100 000 Old_age Always - 0 199 UDMA_CRC_Error_Count 0x000b 100 100 050 Pre-fail Always - 0 218 Unknown_Attribute 0x000b 100 100 050 Pre-fail Always - 0 231 Temperature_Celsius 0x0013 100 100 000 Pre-fail Always - 94 233 Media_Wearout_Indicator 0x000b 100 100 000 Pre-fail Always - 50171 240 Unknown_SSD_Attribute 0x0013 100 100 000 Pre-fail Always - 0 241 Total_LBAs_Written 0x0012 100 100 000 Old_age Always - 12213 242 Total_LBAs_Read 0x0012 100 100 000 Old_age Always - 321 244 Unknown_Attribute 0x0002 100 100 000 Old_age Always - 187 245 Unknown_Attribute 0x0002 100 100 000 Old_age Always - 264 246 Unknown_Attribute 0x0012 100 100 000 Old_age Always - 12905344
Raw_Read_Error_Rate – means the number of read errors.
Throughput_Performance – overall disk performance.
Spin_Up_Time – time to drive up to the operating speed.
Reallocated_Sector_Ct – number of redistributed (damaged) sectors.
Power_On_Hours – the number of hours that the disk was working.
Power_Cycle_Count – number of disk on/off.
Program_Fail_Count_Chip – number of write errors in flash memory.
Reported_Uncorrect – hardware ECC errors that can not be fixed.
Power-Off_Retract_Count – number of emergency shutdowns.
Temperature_Celsius – the temperature of the disc in degrees Celsius.
Media_Wearout_Indicator – the health indicator of the disc, if it is below 10, then the disc should definitely be replaced.
Total_LBAs_Written – LBA records.
Total_LBAs_Read – LBA reads.
There may also be other attributes:
Start_Stop_Count – number of starts/stops of the spindle.
Seek_Error_Rate – number of positioning errors.
Spin_Retry_Count – number of retry attempts.
Reallocated_Event_Count – number of sector redistribution operations.
Offline_Uncorrectable – number of faulty sectors.
Flying height – height between the head and the surface of the disc.
Disk Shift – the distance of the disc block displacement from the spindle, can change for example after the falls.
G-Sense Error Rate – errors due to external loads/drops.
RAID arrays are necessary to improve the reliability of data storage and increase the speed of working with disks by combining multiple disks into one large one. RAID arrays can be either hardware, firmware or software.
I will describe several types:
RAID 0 (stripe) – The mode is only for improving performance when reading/writing does not increase reliability. The user has access to the whole volume of disks, if one of the disks fails, the array is usually destroyed and data recovery is almost impossible.
RAID 1 (mirror) – On all disks the recording is performed synchronously, they completely duplicate each other. Half of the disk space is available to the user. Increases performance only when reading, but this is a very reliable way to protect information. The minimum number of disks is 2.
RAID 10 (RAID 1+0) – This is an array of RAID0 from RAID1 arrays. Fast as RAID0 and reliable as RAID1. The minimum number of disks is four and their number should be even. Half of the disk space is available to the user.
RAID 0 + 1 – RAID1 array from RAID0 arrays. Not popular, since the advantages are worse than RAID 10.
RAID 1E – Similar to RAID10 using an odd number of disks and a minimum of 3.
RAID 5 – User-accessible space is reduced by one disk, reliability is lower than RAID 1, performance is increased when reading and writing as in RAID 0. If one of the disks fails, the data can be restored. The minimum number of disks is 3.
RAID 6 – Similar to RAID 5, including speed, but a little more reliable. The space available to the user is reduced by two disks, the information is not lost when two disks fail. The minimum number of disks is 4.
I personally prefer to use RAID 1 and RAID 6.
FTP can work both in the active mode and in the passive mode.
In active mode, the client performs a control connection with the server, and the server makes a connection to the client for data transfer.
The passive control connection and data connection are made by the client himself.
Under the control connection is meant authentication and command transmission.
The control connection is executed by the client in both cases equally, from the client side from the dynamic TCP port 1024-65535 to the server port 21.
In the active mode after the control connection from the client, the FTP server connects to the client’s dynamic port 1024-65535 from its TCP port 20 for data transfer.
In the passive mode after the control connection from the client, the FTP server tells the client the number of the dynamic TCP port 1024-65535 to which it can be connected to the client for data transmission.