Linux/Tools

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A

alias

alias: manage command aliases

To list aliases:

alias
alias [ALIAS]
alias -p [ALIAS]

To create alias:

alias [ALIAS]="[COMMAND]"

To remove alias:

unalias [ALIAS]

CentOS 5 Examples:

alias cp='cp -i'
alias l.='ls -d .* --color=tty'
alias ll='ls -l --color=tty'
alias ls='ls --color=tty'
alias mv='mv -i'
alias rm='rm -i'
alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'
alias ls='ls -CF --color=tty'

To pass a parameter to alias, use a function instead: [1]

function foo() { /path/to/command "$@" ;}

B

badblock

badblocks - search a device for bad blocks

Non Destructive read test:

badblocks -s /dev/sdb
# -s show

Destructive write test:

badblocks -s -w -t 0xff /dev/sdb
# -s show, -w write, -t test pattern

bc

bc - An arbitrary precision calculator language

Note: Default scale is 0, which means no decimal

echo "scale=2 ; 1/2" | bc
echo '(1 + sqrt(5))/2' | bc -l
echo 'pad=20; min=64; (100*10^6)/((pad+min)*8)' | bc    # This shows max FastE packet rate:
echo 'obase=16; ibase=10; 64206' | bc    # Base conversion (decimal to hexadecimal)
seq 100 | (tr '\n' +; echo 0) | bc       # Add a column of numbers.
echo 'ibase=16; 2DEC' | bc               # Base conversion (hexadecimal to default decimal)
echo 'obase=16; ibase=10; 64206' | bc    # Base conversion (decimal to hexadecimal)
echo 'obase=10; ibase=16; 2DEC' | bc     # Base conversion (hex to dec)

Or just use python!

echo "print 10 / 2.0" | python

C

cut

cut - remove sections from each line of files

echo "one,two,three" | cut -f 1 -d ","  # one
echo "one,two,three" | cut -b 1-2  # on
echo "one,two,three" | rev | cut -d , -f 1 | rev  # three (last field)

other cool alternatives: [2]

echo "one two three" | awk '{print $NF}'  # three (last field)
echo "one,two,three" | awk -F, '{print $NF}'  # three (last field)
echo "/string/to/cut.txt" | awk -F'/' '{for (i=1; i<NF; i++) printf("%s/", $i)}'
awk -F, '{print $NF}' file
echo $LINE | grep -o '.*/'
basename /dev/sdb  # sdb
dirname /dev/sdb  # /dev

D

dmesg

dmesg - print or control the kernel ring buffer

Display kernel ring:

dmesg

Clear kernel ring:

dmesg -c

Initial kernel ring at boot is saved to:

/var/log/dmesg

Kernel ring is also logged to:

/var/log/messages

du

du - estimate file space usage

Summarize disk usage of each FILE, recursively for directories.
du --si
du -B M
du --max-depth=1
du -c dir1 dir2  # combined total

---

Find large files

Print largest files and size in bytes

find . -xdev -printf '%s %p\n' |sort -nr | head -20

find out top 10 largest file/directories is taking up the most space in a /var directory/file system:

du -a /var | sort -n -r | head -n 10

more human readable output try:

du -ks /var | sort -n -r | head -n 10

References:

E

F

G

H

I

J

K

L

less

less - opposite of more

cat /etc/passwd | less

Case insensitivity

less -i [FILE]  # --ignore-case

Case sensitivity can be toggled within the program by typing "-i". [3]

ln

ln - make links between files

Symbolic link:

ln -s [TARGET] [ [LINK] ]

Hard link:

ln [TARGET] [ [LINK] ]

Dereference links:

readlink [link]  # best option
ls -l [link] | awk '{print $11}'  # ok option
file [link] | awk '{print $5}  # includes some ugly quotes

To find all hard links to a file:

find [BASEPATH] -xdev -samefile [LINK]

logger

logger - a shell command interface to the syslog(3) system log module

Log message to syslog

logger "message"
logger -t DNS-Made-Easy -s "Problem updating DNS record."
logger -t mail.info test

M

mkinitrd

mkinitrd - is a compat wrapper, which calls dracut to generate an initramfs

mkinitrd [image] [kernel-version]
  -f   # overwrite if image exists
  -v   # verbose

mkfs

mkfs.vfat

Install:

yum install dosfstools

vfat:

mkfs -t vfat /dev/sdg1
fdisk /dev/sdb  # n p 1 enter enter t 1 c w (part type: 0b or 0c)
mkfs.vfat -F 32 /dev/sdb1    # or mkfs.msdos
mkfs.vfat -F 32 /dev/sdb1 -n MOVIES    # or mkfs.msdos

partition type:

b  W95 FAT32         # BIOS INT 13 - Partitions up to 2047GB
c  W95 FAT32 (LBA)   # Extended-INT13 equivalent of 0b

"0x0b (FAT32 without LBA) uses the old BIOS INT 13 which means it can address a maximum of 7.8GB disk space" [4]

modinfo

modinfo - program to show information about a Linux Kernel module

$ modinfo skge
filename:       /lib/modules/2.6.18-92.1.18.el5/kernel/drivers/net/skge.ko
version:        1.6
license:        GPL

mount

mount /dev/sdb1 /mnt

N

nice

Nice and ReNice

-20 high priority
+19 low priority

A high nice value means a low priority for your process: you are going to be nice. A low or negative value means high priority: you are not very nice. The range of allowable niceness values is -20 to +19.

renice [5]

Renice alters the scheduling priority of one or more running processes.
# change the priority of process ID's 987 and 32, and all processes owned by users daemon and root.
renice +1 987 -u daemon root -p 32


$ nice -n 5 ~/bin/longtask   # Lowers priority (raise nice) by 5
$ sudo renice -5 8829        # Sets nice value to -5
$ sudo renice 5 -u boggs     # Sets nice value of boggs's procs to 5 


References:

nohup

nohup - run a command immune to hangups, with output to a non-tty

nohup [APPLICATION] &

Make sure to add the '&' to put the process into the background [6], or you will have to do it manually with:

[ctrl]+z
jobs
bg %1

To nohup a running process: [7]

[ctrl]+z
jobs
bg %1
disown %1

O

P

parted

GNU Parted - a partition manipulation program

Used by OpenELEC to create SD card partitions: (create_sdcard)

DISK = /dev/sdh

# writing new disklabel on $DISK (removing all partitions)...
parted -s /dev/sdh mklabel msdos

# creating partitions on $DISK...
parted -s "$DISK" unit cyl mkpart primary fat32 -- 0 16
parted -s "$DISK" unit cyl mkpart primary ext2 -- 16 -2

# make partition active (bootable)
parted -s "$DISK" set 1 boot on

# tell kernel we have a new partition table
partprobe "$DISK"

# create filesystem
# creating filesystem on $PART1...
mkfs.vfat "$PART1" -I -n System
# creating filesystem on $PART2...
mkfs.ext4 "$PART2" -L Storage

# sync disk
sync

printf

printf - format and print data

printf:

printf "%'.2f" var
printf "%'.2d" var
printf "Total Rs.%'.2f" var
printf "Total $.%'.2f" var
printf "%'.2f\n" $x

References:

Q

R

S

scp

scp file user@host:/some/path/
scp user@host:/some/path/file /some/path
scp -P 22 file user@host:/some/path/
scp -i myidentity file user@host:/some/path/

smartctl

SMART Tools

Smartmon Tools

Get Disk Information:

smartctl -a /dev/sda

Turn on SMART:

smartctl -s on -o on -S on /dev/hda
# -s on  # Enable/disable SMART on device (on/off)
# -o on  # Enable/disable automatic offline testing on device (on/off)
# -S on  # Enable/disable Attribute autosave on device (on/off)

How long has this disk (system) been powered on in total:

smartctl -A /dev/sda | grep Power_On_Hours
smartctl -i /dev/hda
smartctl -H /dev/hda
smartctl -t short /dev/hda
smartctl -l selftest /dev/hda

References:

ssh

ssh user@host
ssh user@host some_command
ssh -p 22 user@host
scp -i myidentity user@host

---

Keep Alive:

# send keep alive every 30 seconds
ssh -o ServerAliveInterval=30 user@host

References:

strace

strace - trace system calls and signals

List files opened by command:

strace -e trace=open vmkload_mod -s iomemory-vsl > /dev/null

Summarise/profile system calls made by command:

strace -c ls >/dev/null

List system calls made by command:

strace -f -e open ls >/dev/null

T

tar

tar - GNU ‘tar’ saves many files together into a single tape or disk archive, and can restore individual files from the archive.

List tar contents:

tar -tf file.tar

Build tar:

tar -cf file.tar  file1 file2 file3
tar -cf file.tar  folder1
tar -cf file.tar  -C folder1  .     # chdir, so don't include folder in tar
cd folder1 ; tar -cf ../file.tar *  # build tar of current folder, but don't include
tar -cf file.tar  *                 # make archive of all files, will have issues second run

Extract tar:

tar -xf file.tar
tar -xf file.tar  file1           # only extract file1
tar -xf file.tar  -C folder1      # chdir, then extract

Options:

-h, --dereference	# dereference links: (copy actual file, not link)
-A, --catenate, --concatenate	# append tar files to an archive
-c, --create		#create a new archive
-t, --list		#list the contents of an archive
-u, --update		#only append files that are newer than the existing in archive
-x, --extract, --get	#extract files from an archive
-C, --directory DIR	# change to directory DIR

Excludes:

# archive
tar --exclude='./folder' --exclude='./upload/folder2' somefolder -zcvf /backup/deploy.tgz
# extract
tar -xvf deploy.tgz --exclude '.htaccess'

time

time: time a process

Time a process:

time [process]

Example:

$ time sleep 10
real    0m10.006s
user    0m0.001s
sys     0m0.003s

Capture time:

$ ( time sleep 10 ) 2>&1 1>/dev/null | grep real | awk '{print $2}' 
0m10.011s

Convert to Seconds:

OUTPUT=$( ( time staf $IPPREFIX$1 ping ping ) 2>&1 )
FULLTIME=$( echo "$OUTPUT" | grep real | awk '{print $2}' | awk -F . '{ print $1 }' )
MTIME=$( echo $FULLTIME | awk -F 'm' '{print $1}' )
STIME=$( echo $FULLTIME | awk -F 'm' '{print $2}' )
TOTAL_SECONDS=$(( $MTIME * 60 + $STIME ))

touch

touch - change file timestamps

create file:

touch [file]

set file time:

touch -c -t 0304050607 [file]
touch -d "2004-02-27 14:19:13.489392193 +0530" [file]
touch --date="2004-02-27 14:19:13.489392193 +0530" [file]
touch --date "2004-02-27 0:0:0" [file]  # 1 hour behind?

tr

tr - translate or delete characters

Convert to upper or lower case:

... | tr [:lower:] [:upper:]
... | tr [:upper:] [:lower:]

tree

tree - list contents of directories in a tree-like format.


Directory tree:

tree

Shell script way: [8]

ls -R | grep ":$" | sed -e 's/:$//' -e 's/[^-][^\/]*\//--/g' -e 's/^/   /' -e 's/-/|/'

Output as CSV file: [9]

find | sed -e's/"/\\"/g' -e's/^..//' -e's/\//","/g' -e's/^/"/' -e's/$/"/' > /tmp/listing.csv

http://www.centerkey.com/tree/tree.sh:

#######################################################
#  UNIX TREE                                          #
#  Version: 2.3                                       #
#  File: ~/apps/tree/tree.sh                          #
#                                                     #
#  Displays Structure of Directory Hierarchy          #
#  -------------------------------------------------  #
#  This tiny script uses "ls", "grep", and "sed"      #
#  in a single command to show the nesting of         #
#  sub-directories.  The setup command for PATH       #
#  works with the Bash shell (the Mac OS X default).  #
#                                                     #
#  Setup:                                             #
#     $ cd ~/apps/tree                                #
#     $ chmod u+x tree.sh                             #
#     $ ln -s ~/apps/tree/tree.sh ~/bin/tree          #
#     $ echo "PATH=~/bin:\${PATH}" >> ~/.profile      #
#                                                     #
#  Usage:                                             #
#     $ tree [directory]                              #
#                                                     #
#  Examples:                                          #
#     $ tree                                          #
#     $ tree /etc/opt                                 #
#     $ tree ..                                       #
#                                                     #
#  Public Domain Software -- Free to Use as You Like  #
#  http://www.centerkey.com/tree  -  By Dem Pilafian  #
#######################################################

echo
if [ "$1" != "" ] #if parameter exists, use as base folder
  then cd "$1"
  fi
pwd
ls -R | grep ":$" | \
  sed -e 's/:$//' -e 's/[^-][^\/]*\//--/g' -e 's/^/ /' -e 's/-/|/'
# 1st sed: remove colons
# 2nd sed: replace higher level folder names with dashes
# 3rd sed: indent graph three spaces
# 4th sed: replace first dash with a vertical bar
if [ `ls -F -1 | grep "/" | wc -l` = 0 ]  # check if no folders
  then echo " -> no sub-directories"
  fi
echo
exit

U

ulimit

ulimit - Provides control over the resources available to the shell and to processes started by it, on systems that allow such control.

The default maximum open files (file descriptors) on a Redhat Linux system is 1024 per session. This is set here:

/etc/security/limits.d/90-nproc.conf

See all of the current soft limits: [10]

ulimit -a
ulimit -Sa

See all of the current hard limits: [11]

ulimit -Ha

To see the current session limit:

ulimit -n

To see the system limit:

cat /proc/sys/fs/file-max

To set the max to half the system limit:

ulimit -n $(( `cat /proc/sys/fs/file-max` / 2 ))


Umlimited?

The system file descriptor limit is set in /proc/sys/fs/file-max. The following command will increase the limit to 65535:

echo 65535 > /proc/sys/fs/file-max

You should then be able to increase the file descriptor limits using:

ulimit -n unlimited

This did not work for me.


A bash forkbomb [12]

$ :(){ :|:& };:

References:

V

W

X

Y

Z

keywords