Bash Index : P - The 'P' Bash commands : description, flags and examples

useradd bob; grep bob /etc/shadow

bob:!:17547:0:99999:7:::	new passwordless account is disabled

passwd bob; grep bob /etc/shadow

Enter new UNIX password: 123456
Retype new UNIX password: 123456
passwd: password updated successfully
bob:$6$OXeqopLJ$8xicqHptSgZ/JuUFFV1az4keocSKSa53bAC9BFdMRqn1d92ltyXI1Mc2Vx2a708Jhsvszeduuvm/49/uPp6FP1:17547:0:99999:7:::	the encrypted password

passwd -l bob; grep bob /etc/shadow

passwd: password expiry information changed.
bob:!$6$OXeqopLJ$8xicqHptSgZ/JuUFFV1az4keocSKSa53bAC9BFdMRqn1d92ltyXI1Mc2Vx2a708Jhsvszeduuvm/49/uPp6FP1:17547:0:99999:7:::	the extra ! shows it's locked

passwd -u bob; grep bob /etc/shadow

passwd: password expiry information changed.
bob:$6$OXeqopLJ$8xicqHptSgZ/JuUFFV1az4keocSKSa53bAC9BFdMRqn1d92ltyXI1Mc2Vx2a708Jhsvszeduuvm/49/uPp6FP1:17547:0:99999:7:::	unlocked

passwd -d bob; grep bob /etc/shadow

passwd: password expiry information changed.
bob::17547:0:99999:7:::	empty password

passwd bob; grep bob /etc/shadow

Enter new UNIX password: 123456
Retype new UNIX password: 123456
passwd: password updated successfully
bob:$6$nAmbe8KT$Dl3GXxWEjhRhuCPUA7dFyA7MZvAXtkAVJm14n0asq9OVioh1b1OK2mE0pYmTJqKtnY.kz5jGiaEJhs1JAEkTi.:17547:0:99999:7:::	password is back. Same clear text, different crypted text

passwd -dl bob; grep bob /etc/shadow

passwd: password expiry information changed.
bob:!:17547:0:99999:7:::	now empty AND locked

passwd -u bob; grep bob /etc/shadow

passwd: unlocking the password would result in a passwordless account.
You should set a password with usermod -p to unlock the password of this account.
bob:!:17547:0:99999:7:::	no change : will not make a passwordless account

passwd bob; grep bob /etc/shadow

Enter new UNIX password: 123456
Retype new UNIX password: 123456
passwd: password updated successfully
bob:$6$fyixHXv.$YT56pM8ExEtfsght7E8cxyP1EYmLwrBp1mW8sJ/ZVn8J.K0G9gQUC7mMycqXM0lAda1/.3KU.4Q56CtT8OtcH/:17547:0:99999:7:::	password added

usermod --expiredate 1 bob; grep bob /etc/shadow

bob:$6$fyixHXv.$YT56pM8ExEtfsght7E8cxyP1EYmLwrBp1mW8sJ/ZVn8J.K0G9gQUC7mMycqXM0lAda1/.3KU.4Q56CtT8OtcH/:17547:0:99999:7::1:

userdel -r bob; grep bob /etc/shadow

(nothing)

• parted
• (parted) select /dev/sdb

  Utilisation de /dev/sdb

• (parted) mkpart primary ext2 0 -0

  Avertissement: L'alignement de la partition ainsi définie n'est pas optimal au niveau performance.
  Ignorer/Ignore/Annuler/Cancel?

  Alignment can NOT be optimal since we're using the whole disk.
  Ignore

  (nothing)

• (parted) print

  Modèle: VMware Virtual disk (scsi)
  Disque /dev/sdb : 21,5GB
  Taille des secteurs (logiques/physiques): 512B/512B
  Table de partitions : msdos
  Disk Flags:
  
  Numéro	Début	Fin	Taille	Type	Système de fichiers	Fanions
   1	1049kB	21,5GB	21,5GB	primary

• (parted) rm 1

  (nothing)

• (parted) print

  Modèle: VMware Virtual disk (scsi)
  Disque /dev/sdb : 21,5GB
  Taille des secteurs (logiques/physiques): 512B/512B
  Table de partitions : msdos
  Disk Flags:
  
  Numéro	Début	Fin	Taille	Type	Système de fichiers	Fanions

• (parted) quit

Create a partition using the whole disk

Check

Delete a partition

Well, it's all in the error message : /dev/sdc has a disk label parted is unable to handle.

parted -a optimal -s /dev/sdc -- mklabel msdos mkpart primary ext2 0 -1s

• parallel [options] [command [arguments]] < list_of_arguments
• parallel [options] [command [arguments]] ( ::: arguments | :::+ arguments | :::: argfile(s) | ::::+ argfile(s) ) ...

is an ERE for matching against

• the process name (i.e. binary name, default behavior)
• the whole command line, with -f

Let's imagine there is a process running somewhere :

• get its PID :
  pgrep -f "tail.*someFile"
• kill it :
  pkill -f "tail.*someFile"

sends a flood (-f) unfragmented (-D), data-loaded (-s) ping. The 1472 payload bytes are the maximum since we're sending an unfragmented packet on a LAN, where the MTU is 1500 bytes.

• 1472 (payload) + 8 (IP headers) + 20 (ICMP ECHO REQUEST) = 1500 bytes
• When receiving such input, an XP host has its network about 75% busy, and CPU about 30-40% busy.

By default, ICMP_ECHO_REPLY is disabled in XP SP1.

You'll often get the Destination host unreachable error message with ping. This actually means you are 1 step ahead of "no response at all", which is good news but does not help much either . To further investigate, consider traceroute.
(see also)

Considering 2 files :

• file1

  file1, line1
  file1, line2
  file1, line3

• file2

  file2, line1
  file2, line2
  file2, line3

file1, line1	file2,line1
file1, line2	file2, line2
file1, line3	file2, line3

Basic passwords : alphanumeric n-characters long ([a-zA-Z0-9]{n}) :

Truly secure passwords : strong but hard to memorize :

Intermediate passwords : stronger than basic ones but still possible to memorize + have distinct passwords for all accounts + change them regularly :

This is for fun only : the words generated with the methods below —albeit created with a password generator— must NOT be used as passwords. Indeed, the syntax rules (lowercase characters only, patterns of alternating consonants / vowels) makes them extremely poor passwords.

single word :

wordLength=10; generateOneWord() { pwgen -0 -1 -A "$wordLength" | grep -Ei '^[b-df-hj-np-tv-xz][aeiouy]{1,2}[b-df-hj-np-tv-xz][aeiouy]{1,2}[b-df-hj-np-tv-xz]{1,2}'; } ; until generateOneWord ; do true; done

multiple words :

wordLength=10; nbWordsToGenerate=12; nbGeneratedWords=0; generateOneWord() { consonant='[b-df-hj-np-tv-xz]'; vowel='[aeiouy]'; pwgen -0 -1 -A "$wordLength" | grep -Ei "^($consonant$vowel{1,2}$consonant$vowel{1,2}$consonant{1,2}$vowel{2}|$vowel$consonant{1,2}$vowel{1,2}$consonant{1,2}$vowel{1,2}$consonant)"; } ; until [ "$nbGeneratedWords" == "$nbWordsToGenerate" ] ; do generateOneWord && nbGeneratedWords=$((nbGeneratedWords+1)); done