bash_zsh_linux

# remove specific emails from the postqueue
mailq | tail -n +2 | grep -v '^ *(' | awk  'BEGIN { RS = "" }
                  # $7=sender, $8=recipient1, $9=recipient2
                  { if ($8 == "[email protected]" && $9 == "")
                        print $1 }
               ' | tr -d '*!' | postsuper -d -

# ssh-keygen options
ssh-keygen -t ed25519 -f ssh_host_ed25519_key -N "" < /dev/null
ssh-keygen -t rsa -b 4096 -f ssh_host_rsa_key -N "" < /dev/null
ssh-keygen -t ed25519 -f ssh_host_ed25519_key -N "" < /dev/urandom
ssh-keygen -t rsa -b 4096 -f ssh_host_rsa_key -N "" < /dev/urandom
ssh-keygen -t ed25519 -a 100 -f ssh_host_ed25519_key
ssh-keygen -t rsa -a 100 -b 2048 -f ssh_host_rsa_key

# convert ssh keys

# from SSH2 to OpenSSH
ssh-keygen -i -f nameofpubkey.pub > newnameofpubkey.pub

# from OpenSSH to SSH2 (rfc4716 format)
ssh-keygen -e -f nameofpubkey.pub > newnameofpubkey.pub

# print human-readable process name
ps rf -opid,cmd -C <process-name> | awk ‘$2 !~ /^[|\\]/ { print $1 }’

# drop this in your .bash_profile to use a default SSH key with the agent
if [ -z "$SSH_AUTH_SOCK" ] ; then
  eval `ssh-agent -s`
  ssh-add
fi

# expanding a linux LVM disk live (no reboot)
tldr; expand disk, fdisk /dev/disk, delete partition 1, create new part, expand till max, w - and then q in fdisk, partx /dev/disk (150gb), xfs_growfs /dev/part1, partx -u

1. expand the disk (through AWS) or attach a new volume (which will become the /root or /disk)

# before moving ahead, for god sakes, make sure the new disk/partition settings match the original disk (or else risk corruption)
2. fdisk -l /dev/disk # take a screenshot, or remember the DISK TYPE 
2a. fdisk /dev/disk #format disk command prompts inc
2b. > m [enter] # FFS read this before proceeding
2c. > d [enter] # will DELETE 'partition 1', assuming that's the one you want to delete
2d. > n [enter] # will create new partition, expand until max, write changes to disk
2e. >> p OR [enter] # will be used as the PRIMARY partition type, or hit ENTER for default
2f. >> 1 OR [enter] # will be used as the partition number to designate, or hit ENTER for default
2g. >> 666 OR [enter] # will be used as the FIRST SECTOR, or hit ENTER for default
2h. >> 9000 OR [enter] # will be used as the LAST SECTOR, or hit ENTER for default
>> `Created a new partition 1 of type 'Linux' and of size 30 GiB. # an example of what the output _should look like_`
2i. > w [enter] # will WRITE CHANGES to the disk
# the output should look akin to:
>> `The partition table has been altered.`
>> `Calling ioctl() to re-read partition table.`
>> `Re-reading the partition table failed.: Device or resource busy`
>> `The kernel still uses the old table. The new table will be used at the next reboot or after you run partprobe(8) or kpartx(8).`
2j. > q [enter] # exit from fdisk
2f. fdisk -l /dev/disk # VERIFY new partition layout

# we touched the disk layout, now to actually expand the disk and update the kernel
3a. partprobe # on centos it will likely fail, so we use partx (which does no real checking)
3b. partx -v /dev/disk #  tell the Linux kernel about the presence and numbering of on-disk partitions
3c. xfs_growfs /dev/xvda1 # grow the filesystem
3d. partx -u /dev/xvda # the true magic that people don't document, update the kernel with new layout

# spinning progress bar
# /usr/bin/scp [email protected]:file somewhere 2>/dev/null &
pid=$! # Process Id of the previous running command

spin[0]="-"
spin[1]="\\"
spin[2]="|"
spin[3]="/"

echo -n "[copying] ${spin[0]}"
while [ kill -0 $pid ]
do
  for i in "${spin[@]}"
  do
        echo -ne "\b$i"
        sleep 0.1
  done
done