CarlHolmberg

• Linux related notes
  • bash
    • sudo -E bash -c '<a shell command>' # preserve user environment (aliases & variables) when issuing a command under sudo.
    • sudo ls -l /proc/$(pidof <process name>) | grep exe # to check which file a process is run from.
    • sudo ls -l /proc/$(pidof <process name>) | grep fd # what files/sockets/etc the process has open.
    • head -c 1G /dev/urandom >myfile # create a file full of rubbish.
    • nohup sudo <command> # protect an elevated process from a console hang up.
  • compressing
    • zip –r filename.zip directory_name # recursively zip a directory
  • git
    • git reset <hash> # make a previous commit the current state.
    • git commit --amend --no-edit # don't pollute the commit log when making heaps of small changes.
    • git push -f origin <branch> # and force that commit to the branch.
    • git branch -d <branch> # delete local branch
  • mongo
    • control
      • sudo systemctl enable mongod.service
      • sudo systemctl start mongod.service
    • shell
      • mongo # if locally hosted
      • show dbs
      • use <dbs name>
      • show collections
      • db.<collection name>( {} ) # equiv to SQL select * from <table>
      • db.<collection name>.find( { <tag>: "<value>" } ) # equiv to SQL select * from <table> where <field> = "<value>"
  • php
    • php -f <file>.php # run script from console.
  • python
    • grip # renders README.md files into html for preview on localhost web service.
    • python3 setup.py bdist # create *.tar.gz in the ./dist directory
    • python3 setup.py bdist_rpm # create rpm in the ./dist directory
  • rpm
    • sudo dnf config-manager --add-repo /etc/yum.repos.d/.repo
    • sudo dnf config-manager --set-enabled
    • rpm -qlpv ./path/to/test.rpm # list files in RPM package file.
    • rpm2cpio ./path/to/test.rpm | cpio -idmv # unpack contents of RPM package to working directory.
    • rpm -qp --scripts ./path/to/test.rpm # view un/install scripts for RPM package.
    • rpm --showrc | grep sitelib # show values for options set in rpmrc, look for where pure Perl/Python modules are kept.
    • sudo yum --disablerepo="*" --enablerepo="mpia" list available # list packages available in a single repo.
    • sudo flatpak uninstall --unused # clears out unused app runtime library crap filling up /var.
  • systemd
    • reading logs in systemd
    • journalctl -n 50 | grep sendmail > sendmail.log # get the last 50 system log messages, and filter.
    • /usr/lib/systemd/system/ # location of systemd *.service descriptions.
    • list units: systemctl list-unit-files | grep [disabled|enabled|static]
  • vim
    • :set fileformat=[dos|unix]
    • :set [list|nolist] # to show hidden characters
    • :%s/<find>/<replace>/g # global replace
    • :set [paste|nopaste|pastetoggle] # to control automatic indentation when pasting in code.
    • :set [spell|nospell] # spelling highlighting
    • select: V (start @ line), v (start @ cursor), ctrl-v (start @ column), gv (reselect block), move cursor, then y or d.
    • block comment out: ctrl-v (rect vis sel mode), j for each line, Shift-i, type // (or # or " or ...), Esc key.
    • more block shifting: https://vim.fandom.com/wiki/Shifting_blocks_visually
    • flake-8, a PEP8 format checker for Python files: https://github.com/nvie/vim-flake8
    • hex edit with xxd, enable :%!xxd disable :%!xxd -r
  • cron format: