htop: save configuration

To exit htop and save config in file:

  F10

To find the config file just after you exit:

  find -name '*htoprc*' -mmin -10

Slow loading mysql dump into RDS

It's the PIOPS, stupid. Try cranking them up, e.g. 300GB volume at 3000 IOPS on your RDS instance when you create it.

See if that helps.

I just went from load taking days to load taking only hours.

This is an official AWS collection point for data, so please leave a comment on your experience. jk.

create simple mysql table for testing

CREATE TABLE suppliers (
    SupplierID SMALLINT UNSIGNED ZEROFILL NOT NULL AUTO_INCREMENT,
    SupplierName VARCHAR(40) NOT NULL,
    Phone VARCHAR(14) NOT NULL,
    Email VARCHAR(60) NULL,
    PRIMARY KEY (SupplierID)
 );

INSERT INTO suppliers (SupplierName, Phone, Email) VALUES ('ABCSupplier','1122334455','abc@dicforum.com');

VirtualBox: port forwarding to guest from host

Something weird in the new (2015-06) version.

• Network
• Set "NAT"
• Click "Port Forwarding"
• "Insert new rule" (right-hand nav button)
• Rule 1
• Host IP: 127.0.0.1
• Host port: 2222
• Guest IP: [leave blank]
• Guest Port: 22

To get to guest:

ssh -p 2222 myuser@localhost

where myuser is user you created when you installed Linux OS on to VM.

Connect to remote JMX over ssh and jconsole

ssh -N -f -D 7777 dev-cass-10.mydomain.internal

jconsole -J-DsocksProxyHost=localhost -J-DsocksProxyPort=7777 service:jmx:rmi:///jndi/rmi://localhost:7199/jmxrmi

Stress Linux system: stress-ng

worthy: stress-ng

NOTE: it's the newer/better version of "stress"

Quote:

stress-ng current contains the following methods to exercise the machine:

• CPU compute - just lots of sqrt() operations on pseudo-random values. One can also specify the % loading of the CPUs
• Cache thrashing, a naive cache read/write exerciser
• Drive stress by writing and removing many temporary files
• Process creation and termination, just lots of fork() + exit() calls
• I/O syncs, just forcing lots of sync() calls
• VM stress via mmap(), memory write and munmap()
• Pipe I/O, large pipe writes and reads that exercise pipe, copying and context switching
• Socket stressing, much like the pipe I/O test but using sockets
• Context switching between a pair of producer and consumer processes

Interview: sysadmin

Command line tools

Which tools have you used in below categories? With which options? What do the options perform? (possible answers/options listed after category)

  * network tools

    * iftop: n, N, P
    * lsof: i, p, c, N, P
    * tcpdump: n, host, net, and, or
    * iptables: t, L, n, D
    * dig: txt, mx, a, cname
    * ping
    * traceroute/mtr

  * filesystem tools

    * df: h, a, s, T
    * du: s, h
    * fdisk: l
    * mkfs
    * find: exec, name, type
    * updatedb/locate

  * monitoring tools / process management

    * watch: d, n
    * ps: a, u, x, w
    * htop
    * vmstat: <seconds>
    * sa/sar
    * nice
    * smartctl
    * iostat: <seconds>, x, m


* Filesystems

  * Which are the types of filesystems: ext3, ext4, xfs, brtfs
  * What is an inode? How would you handle a "disk full" error related to inodes usage?


* Networking

  * What is port forwarding and how have you used it?
  * What is CIDR, show examples?
  * What is NAT? How have you used NAT technology?
  * What are the types of protocols? Explain their use. (tcp, udp, icmp)
  * Which hardware/software firewalls have you used? Explain.
  * Have you used VPN technology? Explain what was done and how you were involved.


* AWS

What is your experience with AWS? Detail/diagram projects.

Which AWS technologies have you used?

  * EC2

    * How have you managed AWS servers: API, web interface, command line tools?
    * Which types of instances have you used?
    * How many servers were you responsible for?
    * What is the difference between EBS and ephemeral storage? Pros/cons.

  * EBS

    * Which parameters does volume creation require?
    * What is a snapshot? How are redundant blocks stored for subsequent snapshots?

  * ELB

    * What is the "health check" used for? What are the parameters
    * Have you used SSL with ELB?
    * What are "listeners"?
    * Have you used ELB in conjunction with haproxy. Diagram.

  * VPC

    * How did you use VPC? Have you setup a AWS VPC from scratch?
    * Do you know what a "DHCP option set" is? How is it used?
    * Diagram what subnets were used, which were public, and which private.

  * SES

    * What is a "verified" email or domain in SES?

  * Route 53

    * Have you created a domain in Route 53?
    * Have you maintained DNS records with Route 53?
    * What does Route 53 offer that other DNS services do not?
    * How does Route 53 integrate with AWS ELB technology?

Monitoring

  * CloudWatch

    * How did you use CloudWatch to monitor server health and network use
    * Did you ever setup a CloudWatch email alert? Explain steps involved.

  * Zenoss

    * What are the tools you used in Zenoss
    * How large was the monitored infrastructure?
    * What is a Zenoss event?

  * On-call

    * Talk about your past on-call experiences, and one time handled a major issue
    * What are the available paging services, and which have you used?

Java

  * What experience do you have installing/supporting Java?
  * Explain how you performed JVM monitoring.
  * Tomcat
    * Have you ever supported Tomcat? What were the configurations you were responsible for?
    * What are the core Tomcat configuration files? Log files?
  * What is the Java Heap? How can this be set/modified, and what are the effects? Downsides?
  * What steps would you take to debug/resolve a "Out of Memory" JVM error?

Cassandra

  * Explain your experience with Cassandra. Versions?
  * How many nodes did you support? What percent of the data load was each node responsible for?
  * nodetool: what are the options, and what do they show/perform?
  * Explain how you built a ring from the ground up in the past
  * What steps did you take to monitor your Cassandra nodes?
  * What steps did you take for a node failure?
  * How did you find/get answers to questions you had on the Cassandra techonology?

Google Nexus 4: permanent back panel glass repair for less than a penny

Clear packing tape. Apply single layer everywhere on back panel there isn't a device port. Be creative.

Has worked for me for months to prevent further damage.

Cost less than $ 0.01.

Doesn't look "pro" but neither do $20 - $30 covers from Toys-R-Us and other similar stores.

I actually only covered the area below the camera and to the left of the speak/microphone/whatever with one single piece I had to cut a bit to size.

Cassandra: links to snapshots in one place

Use rsync with '-L' to copy elsewhere.

#!/usr/bin/ruby

require 'fileutils'

mybasedir = '/var/lib/cass'
mydatadir = mybasedir + '/data'
mysnapshotlinksdir = mybasedir + '/snapshots'
FileUtils.remove_dir(mysnapshotlinksdir) if File.exists?(mysnapshotlinksdir)
Dir.chdir mydatadir
mysnapshotdirs = Dir.glob("**/*/")
mysnapshotdirs = mysnapshotdirs.grep(/snapshots\/.+/)
#p mysnapshotdirs

mysnapshots = {}
mysnapshotdirs.each do |mydir|
    mysnapshot = {}
    myparts = mydir.split('/')
    mysnapshot['keyspace'] = myparts[0]
    mysnapshot['cf'] = myparts[1]
    mysnapshot['tag'] = myparts[3]
    mysnapshot['linkdir'] = [mysnapshotlinksdir, mysnapshot['tag'], mysnapshot['keyspace']].join('/')
    mysnapshot['link'] = [mysnapshotlinksdir, mysnapshot['tag'], mysnapshot['keyspace'], mysnapshot['cf']].join('/')
    mysnapshot['target'] = [mydatadir, mydir].join('/')
    #p mysnapshot
    FileUtils.mkpath mysnapshot['linkdir'] unless File.exists?(mysnapshot['linkdir'])
    File.symlink(mysnapshot['target'], mysnapshot['link']) unless File.symlink?(mysnapshot['link'])
end