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Linux

6/13/20

index

Home

special characters

http://userwww.service.emory.edu/~kim/psy770u/Reference/special_characters.html

Install / Fedora

cronjobs

commands

cmd - <opts>

Info (inxi)

cmd --

no options follow

Desktops

rm -- -Fr (remove the file named " -Fr ")

dnf

DNS

firewalld

date

date MMDDhhmm

to set the date and time.

LVM

date +%m

%m (month) %d (day) %y (2-digit year) %Y (4-digit year) (no space after the + )

LVM2

N.Neighbor'd

fedora

setting the time zone >>>

cd /usr/share/zoneinfo/America/

http://technology.mattrude

cp Chicago /etc/localtime

Wireless

note: nice reference site (

Services

fedora 20

setting the time zone >>>

timedatectl list-timezones

http://www.server-world.inf

Sys Jour

timedatectl set-timezone Asia/Tokyo

timedatectl status

month day

cat

cat /var/log/secure.log* | grep 'Failed password' | grep sshd | awk '{print $1,$2}' | sort | uniq -c

cat /var/log/auth.log* | grep 'Failed password' | grep sshd | awk '{print $1,$2}' | sort | uniq -c

cat /var/log/secure* | grep 'authentication failure' | awk '{print $1,$2}' | sort | uniq -c

cat /var/log/auth.log* | grep 'authentication failure' | awk '{print $1,$2}' | sort | uniq -c

cat /var/log/secure* | grep 'Failed password' | sort | uniq -c

show failed SSH logins by date (look in all "secure*" files)

cat /var/log/secure* | grep 'authentication failure' | sort | uniq -c

cat /var/log/messages.1 | grep 'could not send mail' | wc -l

the number of couldn't email entries

cat /var/log/messages.1 | grep 'could not send mail' | awk '{print $1,$2}' | sort | uniq -c

the number of couldn't email entries by Month and Day

chmod

chmod u+s /usr/sbin/hddtemp

When the setuid bit is used, the behavior described above it's modified so that when an executable is launched,

it does not run with the privileges of the user who launched it, but with that of the file owner instead.

https://linuxconfig.org/how-to-use-special-permissions-the-setuid-setgid-and-sticky-bits

du -s -k * | sort -n -r

var/adm/messages

du .

var/log/syslog

du -s *

env

du -h --max-depth=1 /var/log | sort -rh | head -4

du -h --max-depth=1 /var/www/html | sort -rh | head -5

du -h --max-depth=1 /home | sort -rh | head -6

Getting the Size of a Directory

df -hT

human readable and Type

df -k (df -h)

find

find . -name '*log*' -type f -mtime +700 -exec rm {} \;

find /var/spool/mqueue -name '*log*' -type f -mtime +700 -exec rm {} \;

find . -name mdh -type d (dir)

find / -name socket.py -type f

find /home/users -name .mailrc -type f -print

grep

http://www.panix.com/~elflord/unix/grep.html#wildcards

"escape sequence"

\ "take the next char literally"

rm -rf one\\dir

grep -v ' \ - \ - '

uses escape sequence

grep -v '\-\-'

throw out lines with -- in them.

grep ora* *.log

find ora in all log files

grep " 478 " *.txt

find <space 478 space> in all .txt files

.gz files

gunzip file.gz

uncompress .gz files

https://www.cyberciti.biz/faq/howto-compress-expand-gz-files/

gunzip /var/log/*.gz

uncompress all log files

tar.gz

tar xvzf file.tar.gz

gunzip < file.tar.gz | tar xvf -

tar xvzf file.tgz

gunzip < file.tgz | tar xvf -

ls -l /dev/disk/by-uuid

lsblk

umount /dev/sdb1

Mounting USB drives and FLASH drives

mount

mkdir /mnt/TFLASH (FreeAgent)

mount -t ntfs-3g /dev/sdb1 /mnt/TFLASH

foxconn >

mount /dev/sdf1 /mnt/FreeAgent

mount a "ext 4" usb drive >>>>>>>>>>

had to uplug, then plug back in.

# dmesg <enter>

fdisk

fdisk -l

list

mkfs.ext4

mkfs.ext4 /dev/sdb1

format to a ext4 file system

http://ksearch.wordpress.com/2010/09/29/format-usb-in-linux/

lscpu

display CPU info, such as Architecture

snapshot

ls -alR > file

links

ln -s from to

symbolic linkname actual path/name

ksh

changing the hist file

HISTFILE=$HOME/.history_$$

ssh

ssh -P 8267 192.168.1.67

ssh -P 8268 192.168.1.68

terms

<cnt> <alt> F1 (thru F6)

<alt> F7 (return to desktop)

putting text to a term

echo "some text" > /dev/pts/1

install new software

yum list

yum list "*WORD*"

yum install PACKAGE

installs PACKAGE from the List

tilde stuff ~

~/ go to my home dir

~username go to usernames home dir

CDROM stuff

find out who is using the cdrom

1. get lsof and run it

list open files

2. run fuser -c /cdrom or

file user

fuser -c /cdrom/cdrom0 (whichever appropiate to the mount opint)

solutions to release the cdrom

1. run fuser -ck /cdrom or

fuser -ck /cdrom/cdrom0

2. kill vold and restart it

check for any "dead" processess, "D or Z" when using "ps axf"

/etc/init.d/volmgt stop

If you need to access a floppy or CDROM special device, you may need to turn off the volume manager.

/etc/init.d/volmgt start

To turn the volume manager back on

Mount, copy, and extract CD-ROM content from an IBM proc.

cd /tmp

mount -v cdrfs -o ro /dev/cd0 /mnt

cp /mnt/* /tmp/

umount /mnt

Floppy stuff

very likely you'll need to use rcp vs. cp to get the file you want onto the floppy disk.

vold &

volcheck -v

cd /floppy/floppy0

eject (cd out of the floppy directory first)

while [ 1 ] ; do

After Power Outage

date

restart:

ls -l

Apache

sleep 60

Samba

done

mount:

^ c to exit

FreeAgent

cd /var/log

tail -fn0 syslog kern.log debug

Monitoring files in real-time from the command-line.

Misc Stuff

Linux Backup -----> Timeshift

lspci | grep -i eth

(-i ignore case)

last

show logins listed in the /var/log/wtmp file

fail2ban-client ping

check if fail2ban is working (server should respond with "pong")

echo "a snails progress." | mail -v -s snailmessage [email protected]

echo `date` | mail -v -s mess3 [email protected]

mail -v -s "some progress" [email protected] < /home/mdh/test-mail.txt

$ sudo crontab -e

#trim the eMMC once a week

15 0 0 * * /sbin/fstrim / >/dev/null 2>&1

Part 3: 2>&1 file descriptor

>i>

Whenever you execute a program, the operating system always opens three files STDIN, STDOUT, and STDERR as we know

whenever a file is opened, operating system (from kernel) returns a non-negative integer called the File Descriptor.

So 2>&1 simply says redirect STDERR to STDOUT

The file descriptor for these files are 0, 1, 2 respectively.

& means whatever follows is a file descriptor, not a filename.

In short, by using this command you are telling your program not to shout while executing.

What is the importance of using 2>&1?

If you want to produce no output even in case of some error produced in the terminal. To explain more clearly, let's consider the following example:

$ ls -l > /dev/null

For the above command, no output was printed in the terminal, but what if this command produces an error:

$ ls -l file_doesnot_exists > /dev/null

ls: cannot access file_doesnot_exists: No such file or directory

Despite I'm redirecting output to /dev/null, it is printed in the terminal. It is because we are not redirecting error output to /dev/null, so in order to redirect error output as well, it is required to add 2>&1

$ ls -l file_doesnot_exists > /dev/null 2>&1

How-To run a command that will survive terminal close >

https://unix.stackexchange.com/questions/4004/how-can-i-run-a-command-which-will-survive-terminal-close

$ nohup redshift &

$ nohup redshift >/dev/null 2>&1 &

$ redshift &

$ disown

Rsync

"zero out a mailbox"

cat /dev/null /var/spool/mail/root

/var/spool/mail/

cat /dev/null > chrishassell

cat /dev/null > " _____.log"

"implied device null"

clearing out a file

cp > wtmpx

cp /dev/null wtmpx

> /dev/null 2> /dev/null