System Notes Org

Sometimes, a mounted partition does not have enough space, and it may take time to expand the LVM volume, if there is not currently enough physical space available, and a separate team handles storage.  Of course making a separate partition is a more proper fix, and LVM is flexible enough to accommodate the changes, but sometimes space is filling up, and something has to be done right away.  Maybe /var/log, or /opt is filling up, and you did not think ahead to make it a separate partition. As a quick workaround, it is fairly common to use a symbolic link, or as sysadmins affectionately call it, a symlimk. Let's say an application wants to install under /opt, and you are out of space in /opt, but have plenty of space in /app.  You can use a symlink to trick the system into thinking that it is using /opt, when in fact it is using /app/opt. I like to perform a directory move and symlink creation at the same time.  Note that both /opt and /app already exist, but w...

I thought it might be helpful to point out some career resources for those who may be interested, or actively involved in job hunting.   I realize we all  need to update our resume from time to time, and some of you may not have a LinkedIn profile. Here are some learning resources, and some useful links for career research.   Some of you know me as someone who is always promoting self-learning. Learning Resources Paid Learning Sites are often made available by your employer, so check to see if you have a subscription, or if you can expense it (get reimbursed for the expense).  It doesn't hurt to ask. http://www.safaribooksonline.com  -- Huge selection of technical books, videos, seminars, etc. http://www.pluralsight.com   -- High Quality, from overview to advanced topics for programmers http://www.lynda.com   -- High Quality, some topics are not very advanced, but courses are very well done https://skillport.com  -- Books,...

Server Availability cannot always be checked by using ping, since often a secured subnet will not allow traffic back.  That common practice of dropping packets is an attempt to hide servers and provide additional security, but it can make troubleshooting more difficult. Since ssh is typcially running and responding on any linux servers that need to be managed, check_ssh seems to be more practical than the default check_ping as the check_command for each host definition in Nagios. This simple shell script uses a Nagios plugin /usr/local/nagios/libexec/check_ssh to quickly check the status of a server.  One thing to note is that a Nagios installation is not required, just the plugins have to be compiled so the binary can be available to the wrapper script. #!/bin/sh # checkssh.sh # # Author: Scott McClelland # 2017-03-29 # # checkssh, uses Nagios plugin check_ssh # /usr/local/nagios/libexec/check_ssh # # nagios-plugins are downloadable from: # https://www.nagios.org...

OS Fingerprint Scanning Sometimes there is a question about what  OS  is running on a server. There are advanced options from –help, but usually running nmap with -A is enough to tell you exactly what  OS  is running on the server in question. Edit Simple nmap scan, which includes OS detection: nmap -v -A $s Find an Available IP Note that your company may have another system of record, so check there for the final authoritative answer. A quick way to find an IP that is not in  DNS , and not responding to ping, or ssh, is to run an nmap scan of the subnet. Edit Use nmap to find available IPs net=10.1.1.0;p=24;nmap -v -R -sn ${net}/${p} -o /tmp/subnet-${net}-${p}.txt Note : This may scan a large number of IPs, so it may be more convenient to write to a file to analyze later, rather tthan running the scan multiple times. An available IP would be one that shows an IP address with no DNS name, and also “host down....

How to Buy, Accept, or Mine Bitcoin and Other Cryptocurrencies - Quick Intro Buy Bitcoin on an Exchange One easy way to get started with owning bitcoin is to buy some on an exchange, such as Coinbase. I offer this link because I think it is helpful, not just because I could get $10.  Sometimes you can't tell why people recommend things.  I figure, if you plan to sign up anyway, why not save a little money? With this referral link, we each get $10 in bitcoin after the new account is opened, and a trade of $100 or more is completed: https://www.coinbase.com/join/592f371c2ae3540ae4a4eb70 Note that it is not necessary to buy a full coin, but there are commissions for buying and selling, and  mining fees for transfers.   To minimize commissions, try entering different amounts to see how much makes sense, before completing the transaction.  For example, buying $100 of bitcoin may cost as much in commissions as buying $200 worth, or around $3.00.  In 2...

Discover the Switch Port to which the Server is Connected A previous article, Advanced Linux Networking Tools , covered the basic usage of tcpdump and tshark to discover switch ports on a Cisco switch, but there are times a system may be connected to a different brand, or using a different protocol.  Also, wireshark is not always installed, so relying on tshark is not always the most convenient way to get the required info. By default, Cisco uses a proprietary method of communication between switches and routers called Cisco Discovery Protocol (CDP).  There is another protocol called Link Layer Discovery Protocol (LLDP), which used by other brands, so it is useful to list other options. Find switch information First, use ifconfig to find the interface names.  Then, use tcpdump to listen for packets.  Optional:  write the packet capture output to a .cap file, and use tshark to read the output. Cisco Discovery Protocol (CDP) YOUR_INTERFACE=eth0 ...