Unix Code Diary Entries

This is part of the Semicolon&Sons Code Diary - consisting of lessons learned on the job.

• Add timestamps to every line
• Avoid referencing a folder name within code inside that folder
• Awk
• Bash script settings
• Bits about permission bits
• Colored output breaks pipes
• Command grouping and signals
• Cron job basics
• Debugging a 100 percent CPU process
• Detach process
• Detached commands fail too silently
• Difference between sleep and wait
• Do not rely on the the HOME variable being available in system scripts
• Ffmpeg snippets
• File not found errors should provoke thoughts about ownership and permissions
• File systems
• Filepaths are relative to current working directory
• Find a file across entire file system
• Find command
• Get subprocesses to stop
• Get your numerical user id
• Heredoc
• How do keyboards and mice and power buttons work
• How does fork's behavior differ in child process
• How is autofs used in unix init booting
• How to debug too many files open errors
• How to debug with ltrace
• How to diff oneline files
• How to fill RAM in unix
• How to give your program a blank ENV
• How to guess missing dependencies with apt get
• How to keep track of process progress without hanging
• How to read CPU load measures
• How to source file in same dir
• How to tell whether a private key is password protected
• If a file you have permissions for will not delete assume it is a folder
• Ignore illegal byte sequences
• Immutable attributes
• IO select
• Journalctl
• Kill vs term vs int vs quit signals
• Kill with negative numbers
• Killing a parent process does not kill forked child
• Learn to read diff
• List all users on a system
• Ln will work even if file does not exist
• Makefile installer example
• Makefile tricks
• Mount
• My fav jq commands
• Never assume set e works with 3rd party code
• Non iteractive shell
• Output appearing where terminal input should may indicate forgetting to close a pipe
• Overview of systemd daemons
• Pass through scripts can modify paths
• Paths are relative by default
• Permission denied when redirecting to sudo file
• Prefer mkdir p in all scripts
• Primary on octal notation
• Prints errors to STDERR never STDOUT
• Process niceness
• Process substitution
• Properties of exec created processes
• Pseudo devices
• Put sockest and pids in run folder
• Recursive copy woes
• Remove all files in current dir safely
• Rg
• Run command as another user
• Sed
• See what processes share a pipe and what goes through
• SFTP basics
• Sockets
• Sort
• Spawn vs fork
• Sponge
• Ssh setup
• Stick bit
• Sudo changes the PATH
• Sudo may counter intuitivly be the password free option
• Symbolic vs hard links
• Systemctl
• Systemd
• The confusing way ln handles relative paths
• Things to consider when paging your program's output
• Ufw basics
• Understand problematic processes
• Understand seeking
• Understand shims
• Uninstalling one package version does not stop its daemon
• Uniq only makes consecutive items unique
• Use awk over cut when more than one space in cols
• Use braces to group output
• Use nohup for scripts that should continue when you log out of server
• Use rlimit to add soft and hard resource limits on subprocesses you create
• Var tmp vs tmp
• Wait vs (pthread )join
• Wait with a negative pid to wait for any child
• Watch out for ssh rate limits
• What are cgroups
• What are process groups
• What does dbus do
• What does synchronize do
• What is a session leader
• What is the usecase of dev shm
• What is udev for
• When parsing output of pipes connect both STDOUT and STDERR
• Where do processes place runtime data
• Where to place cache files and download files during program run
• Xargs
• Zero byte files may be folders