Wiki/linux.md

Linux

Application

• Update MINE database: update-mime-database /usr/share/mime
• Get MINE Type of specific file: xdg-mime query filetype <file>
• Get default application for a specific MINE type: xdg-mime query default <minetype>

• Find list of MIME types in:: /usr/share/applications

• Music
  • Download video or playlist from YouTube: youtube-dl --extract-audio --audio-format mp3 <VideoOrPlaylistURL>
• Markdown
  • Grip is required pip install grip

Office

• Remove certain pages from PDF: pdft <input.pdf> cat <pages or range> output <output.pdf>
  • Single pages: n m
  • Range of pages: n-m
  • Special pages: start end
• Merge several PDF files: gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/default -dNOPAUSE -dQUIET -dBATCH -dDetectDuplicateImages -dCompressFonts=true -r150 -sOutputFile=<output.pdf> <input1.pdf input2.pdf>
• PDF to PNG in high quality
  • pdftoppm <input.pdf> <outputname> -png
  • pdftoppm <input.pdf> <outputname> -png -f {page} -singlefile
  • pdftoppm <input.pdf> <outputname> -png -r 300
• Rotate PDF page: pdftk <input.pdf> cat <page>-<rotationtype> output <output.pdf>
  • Rotation type: endeast

• Add Margin to PDF: pdfcrop --margin <lMargin> <tMargin> <rMargin> <bMargin> <input> <output>
  • Margin of 27 corresponds to approximately $1$cm
  • If one argument if provided to --margin it is applied to all 4 sides

• Compress PDF: gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/<option> -dNOPAUSE -dQUIET -dBATCH -sOutputFile=<output.pdf> <input.pdf>

  • dPDFSETTINGS=/screen lower quality, smaller size. (72 dpi)
  • dPDFSETTINGS=/ebook for better quality, but slightly larger PDFs. (150 dpi)
  • dPDFSETTINGS=/prepress output similar to Acrobat Distiller Prepress Optimized setting (300 dpi)
  • dPDFSETTINGS=/printer selects output similar to the Acrobat Distiller Print Optimized setting (300 dpi)
  • dPDFSETTINGS=/default selects output intended to be useful across a wide variety of uses, possibly at the expense of a larger output file

• Copy file and show progress: Use rsync as: rsync -ah --progress <src> <dest>
• Untar Archive
  • .tar: tar -C <destFolder> -xvf <myfile>.tar
  • .tar.gz: tar -C <destFolder> -zxvf <myfile>.tar.gz
  • .tar.xz: tar -C <destFolder> -xf <myfile>.tar.xz
  • Add status
    • Simple method: add option --checkpoint=.100 to add a . for every 100 files extracted
    • More complex: pv <myfile> | tar -xz

Pacman

• Install package and update: pacman -Syu <package>
• Remove package and all dependencies: pacman -Rns <package>
• List all packages: pacman -Qe
• Get info about package: pacman -Qi <package>

• Error failed to commit transaction (conflicting files)
  • Check if conflicting file is required by another package: pacman -Qo <fullFilePath>
  • Remove or rename file
• Clear pacman cache pacman -Sc or pacman -Scc
• One or more PGP signatures could not be verified: gpg --recv-keys <key>

System

• Keyboard
  • Change X11 Layout: setxkbmap <layout>
  • Define layouts in: /usr/share/X11/xkb/symbols/<layoutname>
  • Make layout visible to the menu by adding them to: /usr/share/X11/xkb/rules/evdev.xml
  • Change directly in Xorg via /etc/X11/xorg.conf.d/00-keyboard.conf
• Xresources
  • Reload config file: xrdb ~/.Xresources
  • Read config and merge with currently active: xrdb -merge ~/.Xresources
• Other
  • Sudo config: sudo visudo
    • When editor not exported correctly: sudo EDITOR=vim visudo
• Boot Hooks: cat /proc/cmdline
• System Event Handler
  • Basic systemd event options are in /etc/systemd/logind.conf
  • Get acpid key info acpi_listen
  • Create custom event
    • Create listener
      1. Create event listener file at /etc/acpi/events/<someName>
      2. Insert the following content

         event=<eventName>
         action=/etc/acpi/handlers/<handlerName> <parms>
         

      3. Create handler script at /etc/acpi/handlers/<handlerName>
      4. Restart acpid service

• Sound:
  • Mic test: arecord -vv -f dat /dev/null

• BIOS
  • Display detected devices fwupdmgr get-devices
  • Download latest metadata fwupdmgr refresh
  • List available updates fwupdmgr get-updates
  • Install updates fwupdmgr update

• Mount fat drive with user permissions mount <device> <mountPath> -o dmask=000,fmask=111
• Show which process hold a mount: sudo lsof | grep <mountPath>

• Bootable
  • Copy image to drive dd if=<isoPath> bs=4M of=<drive> status=progress

Wifi

• Wpa2 Enterprise connection for ETH network. Credits to https://gist.github.com/mvetsch/9bfdee7c56140eae2baa0be711fc8ded

nmcli connection add \
    type wifi \
    con-name "eduroam" \
    ifname "wl" \
    ssid "eduroam"
    wifi-sec.key-mgmt "wpa-eap" \
    802-1x.eap "ttls" \
    802-1x.identity "[CUT]@student-net.ethz.ch" \
    802-1x.phase2-auth "mschapv2" \
    802-1x.domain-suffix-match "radius-service.ethz.ch"

• EPFL

nmcli connection add \
    type wifi \
    con-name "eduroam-epfl" \
    ifname "wl" \
    ssid "eduroam" \
    wifi-sec.key-mgmt "wpa-eap" \
    802-1x.eap "peap" \
    802-1x.identity "jegraf@student-net.ethz.ch" \
    802-1x.phase2-auth "mschapv2" \
    802-1x.domain-suffix-match "radius-service.ethz.ch" \
    802-1x.system-ca-certs "yes" \


nmcli connection add type wifi con-name eth ifname wlp3s0  ssid "eth" -- wifi-sec.key-mgmt wpa-eap 802-1x.eap ttls 802-1x.identity [CUT]@student-net.ethz.ch 802-1x.phase2-auth  mschapv2 802-1x.domain-suffix-match radius-service.ethz.ch


# activate with
nmcli connection up eduroam --ask
nmcli connection up eth --ask

• Connect to ETH VPN: sudo openconnect https://sslvpn.ethz.ch

Mount luks encrypted lvm partition from live boot

• lvm2 and cryptsetup are required
• Probe required modules sudo modprobe dm-crypt
• Determine the disk path using sudo fdisk -l, lsblk, blkid etc.
• Decrypt volume and mount it to /dev/mapper/<someName> using sudo cryptsetup luksOpen <diskPath> <someName>
• Scan for the LVM volumes sudo vgscan
• Activate volume sudo vgchange -ay <lvmVolume>
• Find the volume sudo lvs
• Mount the volume sudo mount /dev/<lvmVolume> /mnt/
• Mount required volumes and pass the shell to the main system

sudo mount --bind /dev /mnt/dev 
sudo mount --bind /dev/pts /mnt/dev/pts
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo chroot /mnt

Access critical stuff from inside chroot

for i in dev dev/pts sys tmp run proc
do
    mount --bind /$i /mnt/<newChroot>/$i
done

chroot /mnt/<newChroot>

Network not working inside chroot

cp /etc/resolv.conf /mnt/<chroot>/resolv.conf

Forward device to internet

• Add route on device which matches the ip of the host: ip route add default via <HostIP>
• Enable forwarding: sysctl net.ipv4.ip_forward=1
• Add iptables rules:
  • iptables -t nat -A POSTROUTING -o <InternetInterface> -j MASQUERADE
  • iptables -A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
  • iptables -A FORWARD -i <DeviceInterface> -o <InternetInterface> -j ACCEPT

Restore Raid of LVM volumes

• lvm2 is required
• Required modules: dm-mod, raid1
• Assemble RAID mdadm --assemble /dev/md0 /dev/<member1> /dev/<member2>
• Scan for the LVM volumes sudo vgscan
• Activate volume sudo vgchange -ay <lvmVolume>
• Find the volume sudo lvs
• Mount the volume sudo mount /dev/<lvmVolume> /mnt/
• Add raid config mdadm --examine --scan > /etc/mdadm/mdadm.conf

User and Groups

• Change primary group
  • sudo usermod -g <primaryGroup> <user>
• Add group to user
  • sudo usermod -aG <group> <user>
• Reload user after adding to group
  • newgrp <group>

Block websites using hosts file

• Enter the websites into /etc/hosts as follows:

0.0.0.0     <website>
::1         <website>

• Flush DNS cache by restarting nscd and dnsmasq

Networking

• Show ports being listened on netstat -plntu
• Show used ports lsof -Pn -i4

Backup

• Remote block device to local:
  • Backup : ssh -C <user@address> 'dd if=/dev/<device>' | dd of=<some_image>.img
  • Restore: dd if=<some_image>.img | ssh -C <user@address> dd of=/dev/<device>

SSH copy and untar after sending

• pv <my.tar.gz> | ssh <address> 'tar yxpf - -C <destDirectory>'

Cleanup

• Find large file: du -hs * | sort -h

Mount partition of disk image created with dd

• Find partition start: fdisk -u -l <my_img>

• Calculate start offset: <start> * 512, where 515 is the block size

• Mount: mount -o loop,offset=<my_offset> <my_img> <my_mountpt>

• Check hash for all files in folder: sha1sum <somePath>/* | sha1sum

• Check hash for all files in tree: find <somePath> -type f -print0 | sort -z | xargs -0 sha1sum | sha1sum

• Check if content of directory has changed: ls -alR --full-time /folder/of/stuff | sha1sum

• mpv play mono: --audio-channels=stereo

• Screensaver stuff:

  • Set screensaver to 10mins: xset s 600
  • Disable screensaver: xset s 0
  • Disable powermanagement: xset -dpms
  • Enable powermanagement: xset +dpms
  • Show current settings: xset q

• Sound on HDMI:

  • Check name of output: pacmd list-cards | grep output\:
  • Set to HDMI: pactl set-card-profile 0 output:hdmi-stereo
  • Set back to internal: pactl set-card-profile 0 output:analog-stereo

• Connect iPhone

  • Install ifuse and libimobiledevice
  • Connect iPhone, unlock and select trust
  • Run idevicepair pair
  • Run ifuse -o allow_other <mountpoint>
    • The mount point should be owned by the user and not root

• Get log from dd by running sudo kill -USR1 $(pgrep ^dd$)

Print

• Server at: http://localhost:631

• Wrong TERM on ssh (Terminal)

  • Copy terminfo to remote: infocmp | ssh <remote> tic -

• Display formatting like \n, \t in less: printf "$(< <myfile>)" | less

• Project dos to linux: `find . -type f -print0 | xargs -0 dos2unix

• See all files an executable touches at start: strace -e openat <ELF>