vickistan.com

#Run iostat to get the average cpu usage every 10 seconds for 10 times:
iostat -x 10 10 >> /home/<user>/iostat.out.$(date +"%Y-%m-%d")

#Run dstat to get cpu stats for cpus 1, 3 and the total:
dstat -C 0,3,total

To run top in batch mode (updating every 3 seconds) and write it to a file in my directory
top -b -d 10 -n 3 >> /home/<user>/top-file

Watch disk usage updating every 3 seconds:
watch -d -n 3 'df -h'

To delete lines 4-12 in Vim:

:4,12 d

To replace the word foo with the word bar starting at the line where the cursor is through the end of the file:

:.,$s/foo/bar/

To remove the spaces in the middle of a pip list output line and replace it with == so it can be used to install (if you have to recreate your pyenv):

:%s/([^ ]+ ) +/\1==/g
:%s/ ==/==/

To remove == and everything after from a pip list so that pip will install the newest version:

:%s/==.*//

To reformat a paragraph in vim:
Use <CTRL-J> to join all lines in the paragraph
:gq

To remove all commented and blank lines from a file:

:g/\v^(#|$)/d

Tar and encrypt:
tar cz <dir>/ | openssl enc -aes-256-cbc -pbkdf2 -iter 10000 -e > out.tar.gz.enc

Decrypt:
openssl enc -aes-256-cbc -d -in out.tar.gz.enc | tar xz

Since RedHat/Ubuntu/Debian’s /proc/cpuinfo has a separate entry for each CPU core, you can use this command to count them:
cat /proc/cpuinfo | grep processor | wc -l

To convert a UTF-8 encoded file to UTF-16, you can use iconv on the command line:

iconv -f utf-8 -t utf-16 oldfile > newfile

To connect to MySQL through a tunnel

Open a tunnel on your local machine listening on localhost:3307 and forwarding everything to the mysqlserver server on port 3306, and doing it all via the ssh service on the gateway machine.

ssh -L 3307:domain.name.of.mysqlserver:3306 username@domain.name.of.gatewayserver

Now start mysql connecting to localhost on the port that you are tunneling mysql from the mysql server.

mysql -u username -p -h 127.0.0.1 -P 3307 databasename

mysql assumes it’s connecting to localhost, but on a non-standard port. In fact, the connection is being made securely to the remote mysql server, via the gateway machine and the local “mouth” of the ssh tunnel on your own machine.

—————————————————

tunnel all outbound E-mail traffic back to my personal server to avoid having to change SMTP servers when I am behind firewalls.

ssh -f user@personal-server.com -L 2000:personal-server.com:25 -N

—————————————————-

to send my Google Talk traffic encrypted through the firewall back to my server at home and then out to Google.

ssh -f -L 3000:talk.google.com:5222 home -N

—————————————————

If you are using an updated openssh package and suddenly can’t connect to sites that you could before the update, you can add an option to your .ssh/config file (create it if you don’t have one).

If you see this error:

Unable to negotiate with 127.0.0.1: no matching key exchange method found.
Their offer: diffie-hellman-group1-sha1

add this:

Host somehost.example.org
KexAlgorithms +diffie-hellman-group1-sha1

If you see this error:

Unable to negotiate with 127.0.0.1: no matching host key type found.
Their offer: ssh-dss

add this instead:

Host somehost.example.org
HostkeyAlgorithms ssh-dss

There are command line versions of these as well.

ssh -oKexAlgorithms=+diffie-hellman-group1-sha1 user@127.0.0.1

ssh -oHostKeyAlgorithms=+ssh-dss user@127.0.0.1

Note: It is worth noting that these weaker cyphers were removed from the configuration for a reason. If there is another way to connect without enabling them, it might be worth considering.