Linux tips

Terms and conditions of use

Basics

SSH keys ("ssh-keygen")

# to generate a 4096 bit SSH RSA key
ssh-keygen -t rsa -b 4096
(make sure to set passphrase)

# recommended to register more than one public keys on the host machine
cat id_rsa.pub >> .ssh/authorized_keys

Remote login via SSH ("ssh")

The followings explain how to login to the host machine (server) remotely from the client machine (your terminal).

# to login with a password
ssh -l [user ID] [host machine]

(Example)
ssh -l masakazu [name].aori.u-tokyo.ac.jp

# to login with a SSH key (if already registered)
ssh -i id_rsa -l [user ID] [host machine]

(Example)
ssh -i ~/.ssh/id_rsa -l masakazu [name].aori.u-tokyo.ac.jp

# convenient to create a "config" file in your local .ssh/ (client machine) 
(Example)
Host [name1].aori.u-tokyo.ac.jp
    IdentityFile    ~/.ssh/id_rsa_host1
    User            masakazu
Host [name2].aori.u-tokyo.ac.jp
    IdentityFile    ~/.ssh/id_rsa_host2
    User            masakazu

# convenient to add the following to your .tcshrc
alias [host name] 'ssh -X -l [user ID] [host (target) machine name]'

# tips to export display with heavy graphics
alisa [host name] 'ssh -X -C -l [user ID] [host (target) machine name]'

Check disk usage ("df", "du")

df -h; df -k  # check the total disk usage
du -h; du -k  # check disk usage of the current directory

Backup ("rsync")

"rsync" is a very powerful and useful command with a capability of incremental backup. Recommended to use "rsync", rather than "scp".

# copy locally
rsync -av [source directory name] [target directory name]  # backup locally
rsync --delete-after -av [source directory name] [target directory name]  # backup locally with the "delete" option

# copy via SSH
rsync -ave ssh [source directory name] [target directory name]  # backup via SSH
rsync --delete-after -ave ssh [source directory name] [target directory name]  # backup via SSH with the "delete" option
rsync --copy-unsafe-links -ave ssh [source directory name] [target directory name]  # copy via SSH including softlinked files

Backup2 ("tar")

# tar without compression
tar cvf [file name].tar [directry name]  # combine directries and files to a single file
tar xvf [file name].tar                  # expand a file to directries and files

# tar with compression
tar cvzf [file name].tgz [directry name] # combine directries and files to a single file and compress
tar xvzf [file name].tgz                 # uncompress and expand a file to directries and files

File permission ("chmod")

You need to understand the command, "chmod", first.

# to change all at once
find . -type d | xargs chmod 755  # change all sub-directories to "755"
find . -type f | xargs chmod 644  # change all files to "644"

Jobs

top                            # check machine status
ps u; ps -f; ps -u[user name]  # list user processes
jobs                           # list background jobs
renice +10 [PID]               # lower CPU use
kill; kill -9 [PID]            # stop background process

Jobs2 ("bg", "fg", "&")

You need to understand the commands, "bg" and "fg", first.

# Start shell script
sh [name].sh
bash [name].bash
tcsh [name].tcsh

# Start shell script as a background process
sh [name].sh &
bash [name].bash &
tcsh [name].tcsh &

# Start shell script as a background process with a log output (recommended)
sh [name].sh >& log.[name] &
bash [name].bash >& log.[name] &
tcsh [name].tcsh >& log.[name] &

control+C                      # cancel a foreground process
control+Z                      # stop a foreground process (change it to background with "bg")

Appendix

convert figure file format

ps2pdf [].eps [].pdf   # eps -> PDF file
convert [].eps [].png  # eps -> PNG file
convert [].eps [].tif  # eps -> TIF file
convert [].eps [].jpg  # eps -> JPEG file

Animation

convert --delay ## [].ps [].gif
convert --delay ## *.png [].gif

ASCII format

nkf --unix dos.txt unix.txt  # convert DOS ASCII format to UNIX ASCII format 
dos2unix [windows file].txt  # DOS to UNIX
unix2dos [linux file].txt    # UNIX to DOS

pLATEX

platex [file name].tex  # complie and create DVI file
dvipdfmx [file name]    # convert to PDF file
evince [file name].pdf  # display PDF file

Format newly added HDD

sudo fdisk -l                 # check disks
sudo mkfs -t ext4 /dev/sd[x]  # format with ext4
sudo mkfs.ext4 /dev/sd[x]     # format with ext4

Others

ls -l | wc -l  # count the number of files in the directory (subtract 1)
rpm -ql [package name]  # find the path of the installed package with "yum"

Root administrator

Create an account for a new user

useradd -m -b /home -g users -s /bin/tcsh -p [password] [user ID]

Add RAID

parted -l

parted /dev/sd[x]
  mklabel gpt
  mkpart
  [Enter]
  xfs
  0%
  100%
  print
  quit

cat proc/partitions

mkfs.xfs /dev/sdc1

mkdir /data2
mount /dev/sdc1 /data2

df -hT

emacs /etc/fstab
  /dev/sdc1 /data2 xfs defaults 0 0