This is a list of simple Linux tips and tricks.

Table of Contents

Permissions and Ownership

Permissions are something that often get in the way for new users but are simple to fix. To see the permissions, you can type ls -l. This shows you the file type (“d” for directory, “-“ for file), owner, group, and other permissions. After that you’ll see the ownership. If you’re having permission error when accessing a file, you may need to change the ownership. To do so you need to use the chown command and you’ll probably need to sudo with it. It follows a format like this:

chown {user} {file}

For the {user} you can put your actual user name (something like jsimonelli) or simply use $USER to retrieve it.

sudo chown $USER my_file

You can also chown an entire directory

chown -R {user} {file}

sudo chown -R $USER my_dir

The quick way to open up a directory to all people is to do chmod -R 0777 my_dir

Searching

Finding Files

There are two primary tools I use to find files on Linux, locate and find. locate is the newer and faster tool, but find is much more universal and can do a lot more, so I generally use find. find looks through the file system while locate looks through a database. This makes locate much faster but you’ll have to update the database with sudo updatedb before you can find new files.

find

find is automatically recursive, so it will search through your subdirectories with you needed to add a -r or -R to it.

find takes the format of: find location comparison-criteria search-term

For example, you could do find /usr/lib -name "*gdal*"

find examples

Find jpg files:

find . -name "*.jpg"

find python core dumps:

find . -name "core.*" - note that this will also probably find non core dump files as well

Deleting with find

You can also find and delete these with find . -name "core.*" -exec rm {} +

Search By Directory or File Type

This will also work for directories. However, if you want to search only for directories, you can specify the type:

find . -type d -name my_dir_name

You can also search for file types, such as:

find . -executable

fd

fd is worth giving a try.

Finding Text within Files

grep

grep is a great tool. The basic usage is grep [flags] [pattern] [filename]

Here are the flags I use most often:

-i ignore case
-n show line numbers
-r recursive (search in folders); capitalize to add symlinks

Here’s a way to find all the files with the word “tensorflow”:

grep -irl 'tensorflow' .

Let’s look at a grep command. Here’s one I find particularly useful:

grep -r password /etc

The syntax of grep consists of four parts.

  1. grep command
  2. optional: option(s)
  3. string to search
  4. file, files, or path to be searched
grep -ir driver *   - done when in the folder
grep -r BBDatasetTrainer *
grep -ir precision_recall_curve /Users/juliussimonelli/Documents/pCloud

If you want to search for text within files, you can use grep:

grep -d recurse "This Text" *

One of the most useful flags for me is -i for ignore case:

grep -i -d recurse "This Text" *

ls

Don’t forget ls can also be a great tool for this. Something as simple as ls | grep rsa to find rsa keys. Note that you don’t need asterisks for this.

Also, this question has a great visualization of what the colors mean in ls

You can, however, also use multiple asterisks with ls: ls file_num_*_of_*

Viewing System Processes

top is the default tool and is great, but for something easier to view, try htop.

Storage

ncdu is a great replacement for du. You might not have ncdu by default so you may have to yum install ncdu. If your storage is getting full:

ncdu -x

Another option for exploring storage is df -h.

apt vs apt-get

Debian-based Linux distributions, like Ubuntu, started using apt.

apt is in many ways a nicer version of apt-get. It takes the most commonly used part.

so apt-get remove package is now apt remove package

Other

Another way to find if a file exists is: [ -e myfile.txt ] && echo "Found" || echo "Not Found"

You can also check if it is a regular file: [ -f myfile.txt ] && echo "Found" || echo "Not Found"

Or a directory [ -d myfiles ] && echo "Found" || echo "Not Found"

tldr

Another package worth checking out is tldr. It’s like man but comes with examples.

Colors

I found this amazing script on AskUbuntu.

eval $(echo "no:global default;fi:normal file;di:directory;ln:symbolic link;pi:named pipe;so:socket;do:door;bd:block device;cd:character device;or:orphan symlink;mi:missing file;su:set uid;sg:set gid;tw:sticky other writable;ow:other writable;st:sticky;ex:executable;"|sed -e 's/:/="/g; s/\;/"\n/g')           
{      
  IFS=:     
  for i in $LS_COLORS     
  do        
    echo -e "\e[${i#*=}m$( x=${i%=*}; [ "${!x}" ] && echo "${!x}" || echo "$x" )\e[m" 
  done       
}

Quickly Adding to Files

Let’s say you want to add something to your .gitignore file, and don’t want to bother with vim at the moment. You can add what you need by typing cat > .gitignore then adding whatever you need. Then hit control + D to return to the bash prompt.

Compressing and Decompressing files

Compress

tar -czvf my_directory.tar.gz /path/to/my_directory

Here’s what those flags mean:

  • -c: Create a compressed file
  • -z: Zip with gzip
  • -v: Verbose mode
  • -f: Specify filename

Decompress

tar -xzvf archive.tar.gz

The only different is that we change the “-c” for Create to “-x” for eXtract

Looking at directories, datasets

tree --filelimit 10 --dirsfirst

Delete old files

Just files

The command is of the form: find /path/to/files* -mtime +5 -exec command {} \;. The number afer mtime is in days, so here’s how you find and delete files older than 5 days:

find . -mtime +5 -exec rm {} \;

Files and folders

find . -mtime +30 -exec rm -rf {} \;

If you just want to find them first, you might want something like this:

find . -mtime +30 -print

Installing

Some packages you’ll have to install through a .deb file. VSCode is this way. The way to install these is:

sudo apt install ./<file>.deb