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CIDR Subnet Mask Cheatsheet

Netmask              Netmask (binary)                 CIDR     Notes
____________________________________________________________________
255.255.255.255  11111111.11111111.11111111.11111111  /32  Host (single addr)
255.255.255.254  11111111.11111111.11111111.11111110  /31  Unuseable
255.255.255.252  11111111.11111111.11111111.11111100  /30    2  useable
255.255.255.248  11111111.11111111.11111111.11111000  /29    6  useable
255.255.255.240  11111111.11111111.11111111.11110000  /28   14  useable
255.255.255.224  11111111.11111111.11111111.11100000  /27   30  useable
255.255.255.192  11111111.11111111.11111111.11000000  /26   62  useable
255.255.255.128  11111111.11111111.11111111.10000000  /25  126  useable
255.255.255.0    11111111.11111111.11111111.00000000  /24 "Class C" 254 useable
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How to reset root password on Linux server

First we need to boot into recovery mode. To do so, restart server and hold Shift down to call up the boot menu. Then select (recovery mode) for the image you are using. Once you get Recovery menu, select root and press Enter. You will be redirected to recovery console.

 root@server1:~#

At this point we need to mount file system, since it is in RO (read-only) mode. To do so, type the following:
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