disks.md

Tricks

Command	Description
dd if=/dev/<sdx> bs=<bs> count=1 | hexdump -C hexdump -C -n <bytes> <dev>	Print hexdump of a drive

Directory indexing

1. Set hashed b-trees to speed up lookup for large dirs: tune2fs -O dir_index /dev/<SDX>
2. Optimize directories (reindexing/sorting and compressing): e2fsck -D /dev/<SDX>

Apply default permissions to folder

chmod g+s <PATH>             # Set gid
setfacl -d -m g::rwx <PATH>  # Set default permission for group to rwx
setfacl -d -m o::rx <PATH>   # Set default for other

Verify: getfacl <PATH>

Source

Reformat disk

1. Reset all data: dd if=/dev/zero of=/dev/<SDX> bs=4096 status=progress
   Calculate block size

2. Create new partition:

   parted /dev/<SDX> mklabel gpt
   parted -a opt /dev/<SDX> mkpart primary <PARTITION> 0% 100%

   <PARTITION> - ext4,fat32

3. Format: mkfs.ext4 /dev/<SDX>

   Option	Description
   -m 0	reserved-blocks-percentage
   -T largefile	usage-type (defined in /etc/mke2fs.conf)

   For FAT: dosfstools

4. Label:

   Filesystem	Command
   EXT	e2label /dev/<SDX> <LABEL>
   FAT	fatlabel /dev/<SDX> <LABEL>

Create swap file

1. Create swap

   fallocate --length 2GiB <SWAPFILE> # Initiate swap
   chmod 600 <SWAPFILE>               # Change permissions
   mkswap <SWAPFILE>                  # Define as swap
   swapon <SWAPFILE>                  # Activate

2. Add to fstab: <SWAPFILE> swap swap defaults 0 0 >> /etc/fstab
3. (Optional) Set swappiness: vm.swappiness=10

Disable swap:

swapoff -a
rm -f <SWAPFILE>

Encrypt drive

Source

1. cryptsetup --key-size 512 luksFormat /dev/sdXX /path/to/key
2. <name> UUID=<UUID> /path/to/key > /etc/crypttab
3. systemctl daemon-reload && systemctl start systemd-cryptsetup@<name>.service

Header backup

cryptsetup luksHeaderBackup /dev/sdXX --header-backup-file header.img
gpg2 --recipient <EMAIL> --encrypt header.img

Resizing LVM partition

Source

# We need to resize the logical volume to use all the existing and free space of the volume group
$ lvm
lvm> lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv
lvm> exit

# And then, we need to resize the file system to use the new available space in the logical volume
$ resize2fs /dev/ubuntu-vg/ubuntu-lv
resize2fs 1.44.1 (24-Mar-2018)
Filesystem at /dev/ubuntu-vg/ubuntu-lv is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 58
The filesystem on /dev/ubuntu-vg/ubuntu-lv is now 120784896 (4k) blocks long.

docker.md

docker volume rm $(docker volume ls -qf dangling=true)
docker rm -vf $(docker ps -aq)
docker system prune -a

gpg.md

Commands

Command	Description
gpg --decrypt <FILE>.sec.asc | gpg --import	Import encrypted secret key
gpg --edit-key <KEY> trust	Trust key
gpg --export -a <KEY> > public.key	Export public key
gpg --armor --export-secret-keys <KEY> | gpg --armor --symmetric --output <FILE>.sec.asc	Export private key and protect with password
gpg --list-packets <FILE>.gpg	Show information about encrypting keys

* <KEY> Can be user's email

Multi-recipient

1. Import the keys with gpg --import <KEY>
2. Echo gpg ids (emails) to .gpg-id
3. Sign all keys: gpg --edit-key <KEY>
   1. lsign
   2. y
   3. save
4. pass init -p <subdir> $(cat /path/to/.gpg-id)

Source

Tricks

Use in headeless machine

export GPG_TTY=$(tty)

Troubleshooting

Unsafe permissions on homedir

chmod 700 ~/.gnupg
chmod 600 ~/.gnupg/*

hacks.md

Handy Commands

Description	Command
Change Nemo terminal	gsettings set org.cinnamon.desktop.default-applications.terminal exec xfce4-terminal
Keyboard configure (Ubuntu)	dpkg-reconfigure keyboard-configuration
Display system info	inxi -Fxz
Convert file encoding	iconv -f SHIFT-JIS -t UTF-8 <INPUT> -o <OUTPUT>
Automatic start-up of user services	sudo loginctl enable-linger <USERNAME>
Clean journal	journalctl --vacuum-size=<SIZE>M
Log into another user	su -s /bin/bash <USERNAME>
Advertise hostname	dhcpcd

Chroot inside LiveCD

sudo mount /dev/sda1 /mnt
sudo mount --bind /dev /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo chroot /mnt

Create monitor

gtf 1280 1024 60                                                # Get options for the resolution & refresh rate
xrandr --newmode "1280x1024_60.00" <OUTPUT-OF-1>                # Setup the new mode
xrandr --addmode VIRTUAL1 1280x1024_60.00                       # Add the new mode to an existing input device
xrandr --output VIRTUAL1 --mode 1280x1024_60.00 --left-of LVDS1 # Activate

PulseAudio Auto Switch

• Automatically switch pulseaudio sink to Bluez
  /etc/pulse/default.pa

  .ifexists module-bluetooth-discover.so
  load-module module-bluetooth-discover
  load-module module-switch-on-connect  # Add this
  .endif

• Auto select A2DP profile (instead of HSP/HFP)
  /etc/bluetooth/audio.conf

  [General]
  Disable=Headset

Ubuntu install specific app version

sudo apt-cache policy ${PKG}
sudo apt-get install ${PKG}=${VERSION}
sudo apt-mark hold ${PKG}

xbindkeys

1. Install: sudo apt-get install xbindkeys xautomation x11-utils
2. Create config: xbindkeys --defaults > $HOME/.xbindkeysrc

Some Useul ones:

#Logitech Mouse Button
"xte 'keydown Control_L' 'key W' 'keyup Control_L'"
   b:13

#Change Language
"xte 'keydown Alt_L' 'key Shift_L' 'keyup Alt_L'"
   control + space

Arch Linux Arm

Error: bsdtar: Ignoring malformed pax extended attribute

Old version of bsdtar on Ubuntu - requires v3.3+.

wget https://www.libarchive.org/downloads/libarchive-3.3.1.tar.gz
tar xzf libarchive-3.3.1.tar.gz
cd libarchive-3.3.1
./configure
make
sudo make install

Confirm via bsdtar --version. If done via sudo need to exit and enter again. source

links.md

Gestures

• https://wdullaer.com/blog/2015/10/08/multitouch-trackpad-gestures-with-touchegg/
• http://ineed.coffee/1068/os-x-like-multitouch-gestures-for-macbook-pro-running-ubuntu-12-10/

tmux

• http://www.hamvocke.com/blog/a-guide-to-customizing-your-tmux-conf/

Lenovo Trackpad Keyboard

• https://github.com/lentinj/tp-compact-keyboard

nfs.md

Packages

• nfs-utils (Arch)
• nfs-kernel-server (Ubuntu)

Server

• Create root just for NFS: /src/nfs
• Bind locations: mount --bind /mnt/src /src/nfs/dest
  fstab: /mnt/src /srv/nfs/dest none bind 0 0

Arch

/etc/exports

Option	Description
ro / rw	Clients read only / read-write access
sync /	Server replies after changes by previous request are written to disk
async	Server does not have to wait
wdelay /	Server delays committing write requests when it suspects another write request is imminent.
no_wdelay	Disable the delay. Can only be enabled if sync is enabled
no_all_squash /	Does not change the mapping of remote users
all_squash	Squash all remote users including root
root_squash /	Prevent root users connected remotely from having root access (squashing remote root privileges)
no_root_squash	Disable root squashing

Command	Description
exportfs -v	View exports
exportfs -arv	Re-export

/etc/nfs.conf

• Restrict share to interface

  [nfsd]
  host=<server-ip/hostname>
  

Ubuntu

/etc/default/nfs-kernel-server

• Disable NFSv3: RPCMOUNTDOPTS="--manage-gids --no-nfs-version 3"

Restarting

sudo systemctl restart nfs-config
sudo systemctl restart nfs-kernel-server

Performance

rsize/wsize

• Check: cat /proc/fs/nfsd/max_block_size

/etc/tmpfiles.d/nfsd-block-size.conf:

w /proc/fs/nfsd/max_block_size - - - - 32768

Client

• showmount -e <server>

Mount

<server>:/path   /path   nfs   <option> 0 0

Options

Mounting

Option	Description
auto/noauto	Will mount/not mount the share until it is accessed
x-systemd.device-timeout	How long before give up mounting (seconds)
x-systemd.idle-timeout	Unmount after idling (seconds)
timeo	Time the NFS client waits for a response before it retries an NFS request. (600 = 60 seconds)
hard/soft	Continue trying forever / stop after retrans
bg/fg	Continue to try mounting / exit with error (when using mount command)

Performance

Option	Description
noatime/nodiratime	Dont record access time to files/dirs
sync	Force flushing when writing data

idmapping

• Both server and client
• Check cat /sys/module/nfs/parameters/nfs4_disable_idmapping

/etc/modprobe.d/nfsd.conf

options nfs nfs4_disable_idmapping=0
options nfsd nfs4_disable_idmapping=0

ssh.md

Commands

Command	Description
ssh -d	Debugging
ssh-keygen	Generate a new pair of keys
ssh-copy-id <remote-user>@<remote-ip>	Copy local public key to a remote machine

sshfs

fstab

sshfs#<USERNAME>@<SERVER_IP>:/server/path   /mnt/<DIR>   fuse   IdentityFile=/home/<USERNAME>/.ssh/id_rsa,defaults,allow_other,default_permissions 0 0

or

<USERNAME>@<SERVER_IP>:/server/path  /mnt/<DIR> fuse.sshfs  noauto,x-systemd.automount,_netdev,reconnect,allow_other,IdentityFile=/home/<USERNAME>/.ssh/id_rsa  0 0

Options:

• uid/gid=1000
• cache=yes
• kernel_cache
• compression=no

For Crouton

echo "sshfs -o IdentityFile=/home/<user>/.ssh/id_rsa,allow_other,default_permissions <username>@<server ip>:/server/path /mnt/<folder>" >> /etc/rc.local

Port forwarding

• A <--> B

• B <--> C

• On B: ssh -NTL <port b>:<ip a>:<port a> <ip a>

• On C: ssh -NTL <port c>:localhost:<port b> <ip b>

users.md

• Add new user: useradd -m <USERNAME>
• Edit users: vipw ; Edit groups: vigr