Application Administration

Learning objectives

• How to install packages
• Where to install packages
• How to run apps as services

Linux app install and upgrade

• Package manager
• Side-load

1. Update package index

sudo apt-get update

2. Find the package name

# apt search {keyword}
apt search "^r-.*" | sort

3. Install target package:

# sudo apt-get install {package-name}
# note: not sure which is better `apt` or `apt-get`
sudo apt install r-base r-base-dev

1. Download

#  with curl, download the right Debian package
export R_VERSION=4.5.2
curl -O https://cdn.posit.co/r/ubuntu-2404/pkgs/r-${R_VERSION}_1_$(dpkg --print-architecture).deb

2. Install

# install the Debian package
sudo apt-get install ./r-${R_VERSION}_1_$(dpkg --print-architecture).deb

Source: Posit Docs here

Configure application

• Read the app’s docs
• Create or modify the file

# create a tmux configuration file
cd ~
touch .tmux.conf

# edit it
vim .tmux.conf

Where to find application files

• Read the app’s docs
• Search in some common places (from the book)
  • /bin, /opt, /usr/local, /usr/bin – installation locations for software.
  • /etc – configuration files for applications.
  • /var – variable data, most commonly log files in /var/log or /var/lib.
• Some other places:
  • ~ in a dotfile (e.g., .tmux)
  • ~/.config/

Edit configuration files

• Read the app’s docs
• Use an editor on the server:
  • Nano
  • Vi(m)

Read logs

• Find them
• Read them
• Search them

From the book:

Most applications write their logs somewhere inside the /var directory. Some activities will get logged to the main log at /var/log/syslog. Other things may get logged to /var/log/<application name> or /var/lib/<application name>.

Print:

• Whole log at once: cat
• Few lines at time: less
• First few lines: head
• Last few lines: tail

# print lines as they are written to the log
tail my_file -f

• Filter lines with regex patterns: grep
• Filter lines with conditions: awk

Running the right commands

• Where is binary
• Whether on path
• How to put on path

Either you know (because you put it here) (e.g. /opt/python3)

Or you can find out

which python3
# /usr/bin/python3

Applications need To run in the the terminal, either:

• Specify the path
• Or it is on PATH

To see PATH, print it:

echo $PATH

Option 1: append app’s path to PATH

# edit and save `.bashrc` to add your new path
export PATH=/my/app/path:$PATH

Option 2: create symlink from app location to an on-PATH place

# create a (soft) symlink from installation in `opt` to a place on PATH
sudo ln -s /opt/R/${R_VERSION}/bin/R /usr/local/bin/R
sudo ln -s /opt/R/${R_VERSION}/bin/Rscript /usr/local/bin/Rscript

Source: Posit Docs here

Running apps as services

• Create a service file
• Enable the service

1. Create file

# move to directory where startup services
cd /etc/systemd/system/

# create a service file
touch my_app.service

2. Populate the contents

[Unit]
Description=My Application Service
After=network.target # Or other dependencies

[Service]
ExecStart=/path/to/your/application/executable # Or a script that runs it
WorkingDirectory=/path/to/your/application/directory
Restart=always
User=your_username # Optional, run as a specific user
Group=your_group # Optional, run as a specific group

[Install]
WantedBy=multi-user.target

Reload configurations:

sudo systemctl daemon-reload

Enable your service

sudo systemctl enable my_app.service

Start the service

sudo systemctl start my_app.service