Useful Linux/Mac Setups

• Install Sun/Oracle's JDK

# First add "contrib" to /etc/apt-sources.list
# Then
apt-get update & apt-get install java-package
make-jpkg /path/to/jdk-*-linux-x64.tar.gz
dpkg -i oracle-java-*_amd64.deb

We use ssmtp to send emails. The following uses Gmail's server.

1. After installing, edit the /etc/ssmtp/ssmtp.conf file

   root=username@gmail.com
   mailhub=smtp.gmail.com:587
   rewriteDomain=
   hostname=fileserver.local
   UseSTARTTLS=YES
   AuthUser=username
   AuthPass=password
   FromLineOverride=YES
   

2. Now edit /etc/ssmtp/revaliases to add accounts that we want to be able to send mails. For example,

   root:nguyenthanhvuh@gmail.com:smtp.gmail.com:587
   auser:nguyenthanhvuh@gmail.com:smtp.gmail.com:587
   

3. Finally, we can test sending mails

   $ echo "test" | mail -v -s "testing ssmtp setup" tnguyen@cs.umd.edu
   $ echo "Do this" | mail -s "Todo" nguyenthanhvuh@gmail.com
   $ echo "A TEST" > afile
   $ mail -s "Todo" nguyenthanhvuh@gmail.com < afile
   

This is for RAID-5 setup, which requires a minimum of 3 drives. The usable space is (number of drives - 1) * size of smallest drive. Here we will use mdm to manage our RAID setup (apt-get install mdadm).

To create new drive partitions in the RAID array, we can use fdisk or parted (if the disk size > 2 terabytes). If use fdisk then choose the partition type to be raid (type fd). Now assume we want to use the 4 partitions sdc1, sdc1, sde1, and sdf1.

# build the RAID array
mdadm --create --verbose /dev/md0 --level=5 --raid-devices=4 /dev/sd[cdef]1

# it will take some time to build the array, we can watch its status with
watch cat /proc/mdstat

#once the array is built, we can check with
mdadm --detail /dev/md0

/dev/md0:
Version : 1.2
Creation Time : Fri Jun 24 15:04:32 2016
Raid Level : raid5
Array Size : 734954496 (700.91 GiB 752.59 GB)
Used Dev Size : 244984832 (233.64 GiB 250.86 GB)
Raid Devices : 4
Total Devices : 4
Persistence : Superblock is persistent

Intent Bitmap : Internal

Update Time : Sat Jun 25 00:34:10 2016
State : clean
Active Devices : 4
Working Devices : 4
Failed Devices : 0
Spare Devices : 0

Layout : left-symmetric
Chunk Size : 512K

Name : GiaoChi:0
UUID : 1d431c63:a9fe7dca:ffb4dca5:58391d2e
Events : 1097

Number   Major   Minor   RaidDevice State
0     8     33    0    active sync   /dev/sdc1
1     8     49    1    active sync   /dev/sdd1
2     8     65    2    active sync   /dev/sde1
4     8     81    3    active sync   /dev/sdf1


# create file extension and mount
mkfs.ext4 /dev/md0
mkdir /MYNEWSTORAGE
# in /etc/fstab
/dev/md0    /MYNEWSTORAGE      ext4    defaults    0    0
# finally mount the array so that we can being to access /MYNEWSTORAGE
mount -av

#edit configuration files so that mdm knows how to assemble the array when the system boots
echo "DEVICE partitions" > /etc/mdadm/mdadm.conf
echo "HOMEHOST fileserver" >> /etc/mdadm/mdadm.conf
echo "MAILADDR username@gmail.com" >> /etc/mdadm/mdadm.conf
mdadm --detail --scan --verbose >> /etc/mdadm/mdadm.conf

1. Generate password-less SSH public key
   1. From a terminal, type ssh-keygen -t rsa and hit Enter on most questions, even when it asks for password, i.e., leave the password blank. This allows to log in account from your machine without requiring password.
   2. The public key is stored at ~/.ssh/id_rsa.pub
   3. Tips:
      • Add you SSH public key to code repo (e.g., Github, Bitbucket). This allows you to modify projects (e.g., push) without having to enter username and password.
      • You can also use this key to ssh into other machine without having to enter password (see password-less login below)

2. Password-less login

   To ssh login the server host without having to enter a password:

   $ cat ~/.ssh/id_rsa.pub | ssh username@host 'cat >> ~/.ssh/authorized_keys'
   

3. Miscs:
   • SSH session disconnected and got stuck: type Enter ~ .

4. Mmulti-hop ssh e.g., ssh to user1@host1:port1 and then ssh to user2@host2:port2 (as user1@host1:).

   # This method uses ProxyJump
   # add the following entry to file ~/.ssh/config
   Host AName
   Hostname host1
   Port port1
   User user1
   ProxyJump user2@host2:port2
   
   $ ssh user2@AName
   # first password asked is for user1@host1, second password asked is for user2@host2.
   
   
   # This second method uses netcat (the nc command) and ProxyCommand
   # add the following entry to file ~/.ssh/config
   Host AName
   Hostname host1
   ProxyCommand ssh -q user1@host1 -p port1 nc host2 port2
   StrictHostKeyChecking no
   UserKnownHostsFile=/dev/null
   
   $ ssh user2@AName
   # first password asked is for user1@host1, second password asked is for user2@host2
   

5. using scp

scp -P port_number username@host:/path/to/file /destination/dir

• using rsync resume file transfer

  rsync --partial --progress --rsh=ssh user@host:/path/to/file .
  

• using sshfs to mount remote directories > source: https://linuxize.com/post/how-to-use-sshfs-to-mount-remote-directories-over-ssh/
  1. Install SSHFS

     • For Debian

       $ sudo apt install sshf
       

     • For Mac

       $ brew cask install osxfuse
       $ brew install sshfs
       

  2. Mount remote directories (tip: use password-less SSH to avoid entering password) shell # sshfs [user@]host:[remote_directory] mountpoint [options] # E.g., $ sshfs username@hostname:/home/dir1 /home/dir1/dir2 $ sshfs localhost:/home/tnguyen/Dropbox local2222/ -C -p 2222

• CPU

  echo '2^2^25' | time -p bc > /dev/null
  time -p echo "scale=5000; a(1)*4" | bc -l
  sysbench --test=cpu --cpu-max-prime=20000 run #apt-get install sysbench
  

• permanent switching capslock and control keys

  #add/replace to /etc/default/keyboard
  XKBOPTIONS="ctrl:nocaps" # Some people prefer "ctrl:swapcaps"
  sudo dpkg-reconfigure -phigh console-setup
  

• Emacs key in XFCE

  $ xfconf-query -c xsettings -p /Gtk/KeyThemeName -s Emacs
  OR
  Menu -> Settings -> Settings Editor -> xsettings -> Gtk -> KeyThemeName,  enter Emacs in the field
  

• Burn videos, e.g., mpg, to DVD (http://www.lamolabs.org/blog/author/slmingol/)

  • convert video with ffmpeg

    ffmpeg -i input.m4v -target ntsc-dvd output.mpg
    

  • do authoring

    dvdauthor --title -o dvd -f output.mpg
    dvdauthor -o dvd -T
    # NOTE: --title sets the title of the DVD, -T sets the table of contents. In both
    #     above commands the -o switch is referencing a directory, NOT the actual dvd.
    

  • roll the .mpg file into an ISO file

    mkisofs -dvd-video -o dvdimage.iso dvd
    # NOTE: mkisofs is making an actual DVD video ISO file using the directory, dvd.
    

  • burn ISO to DVD

    growisofs -speed=1 -dvd-compat -Z /dev/dvd=dvdimage.iso
    NOTE: -speed=1 is for use with lower quality discs, increase as necessary
    NOTE: This approach can be used to convert basically any format (m4v, mp4, etc.) to a DVD. Simply change the input file accordingly.
    

• Note: ntpdate is deprecated, use ntp instead shell sudo service ntp stop sudo ntpd -gq sudo service ntp start
• The -gq tells the ntp daemon to correct the time regardless of the offset (g) and exit immediately (q) after setting the time.

• Add user to sudo shell sudo adduser username sudo
• Change username from olduser to newuser. shell # make sure olduser is not logged in or using any process, e.g., restart and log in as another user. $ sudo usermod -l newuser olduser $ sudo groupmod -n newuser olduser $ sudo usermod -d /home/newuser -m newuser
• Disable users shell passwd -l username to lock , passwd -u username to unlock

• Password Protected Website

  # To protect a directory called 'SecDir' on your website,
  # go to SecDir and create/edit .htaccess file as follows:
  AuthName "MySecDir"
  AuthType Basic
  AuthUserFile /path/to/.htpasswd
  require valid-user
  
  $ htpasswd -c /path/to/.htpasswd guestname #create a passwod
  $ chmod 644 /path/to/.htpasswd   #change permission
  
  # to log in SecDir online, enter username: guestname and passwod: yourpass
  

• Run a local server

  $ cd /path/to/dir     
  $ python -m SimpleHTTPServer #optional, can also enter the port e.g., 8080
  

• Use gh-md-toc, e.g., $ gh-md-toc --insert cmds.md

M-x load-file
C-x k : kill buffer
C-x C-x:  start a a location l,  search for something to go to new location,  then press C-x C-x to return back to l
M-x occur:  search all line with matched regexp
C-x C-r : read only
C-x C-v:  reload file (not technically but it works well)
C-c {  in latex mode to create {}
C-j  insert paragraph break
C-c C-s:  insert section subsection paragraph and label
C-c C-e: insert environment (e.g. figure, equation, list etc)
C-c C-f C-e:  emphasize
C-c %   or  ;  :  comment out the paragraph or line
C-c C-r:  on a highlighted region to latex only that region
C-c C-c:  to run latex.
C-c `:  keep on pressing this to review  errors after running latex
C-/:  undo
C-x k: kill buffer
M-/: autocomplete
M-h : mark entire paragraph
C-x h: mark entire buffer
C-t: transpose 2 letters  , e.g.  letet C-t  => lette
M-t: transpose 2 words,  e.g.,  world hello  M-t  ->  hello word  ;   vu, nguyen M-t  => nguyen, vu  (note: cursor btw the 2 words,  Alt-b to move back a word)
C-x C-t: transpose 2 lines
M-u : uppercase letters
M-c : capitalize letters
C-s C-w:  to the end of the word (handy)
Search and replace
C-s twice to redo the last  search
C-s C-w  search the word under the cursor

;; Windows resize
C-x + : make windows same height/width
C-x - : shrink window to fit content

M-x package-refresh-contents:  to refresh melpa content

;; Tramp: open remote files via ssh
open /ssh:user@host#port:/path

;; Tab
untabify / tabify to convert from tab to space and space to tab.

M-x align-current: To align columns in LaTeX table, highlight the table region, then M-x align-current

• Install cocoAspell (which provides aspell)
• Install the appropriate dictionary (./configure; make; make install)