Linux commands¶
Find latest authenticated IP addresses using authorized_keys:
while read l; do if [[ -n $l && ${l###} = $l ]]; then echo $l; grep `ssh-keygen -l -f /dev/stdin <<<$l | awk '{print $2}'` /var/log/auth.log; echo '---'; fi; done < /home/ubuntu/.ssh/authorized_keys
Append line in file if not exist:
LINE='test'
FILE=/path/to/file
grep -q -F -E "(^$LINE)" $FILE || echo "$LINE" >> $FILE
uniq:
uniq # if lines are repeated - show only one of several these lines
-c # in start of all lines show repeats number and space
-d # show only repeatable lines
-f <num> # ignore first num words (word include only not spaces)
-s <num> # ignore first num chars
-u # show only uniq lines
-i # case-insensitive matching
case (all of syntax from example are true):
case "test1" in
"apple" | "test" ) echo "Apple pie is quite tasty." ;;
"kiwi") echo "New Zealand is famous for kiwi."
;;
"test"*) echo "test* match"
;;
*) echo "matches not found"
;;
esac
# Output:
# test* match
expr:
expr ( 2 + 3 ) # error
expr 2+3 # 2+3
expr 2 + 3 # 5
expr '2 + 3' # 2 + 3
expr "2 + 3" # 2 + 3
expr 6 % 3 # 0
expr 6 / 3 # 2
expr 6 / 3.5 # error
expr 6 \* 3 # 18
expr 3 \> 3 # 0
expr 3 \>= 3 # 1
expr tt = t # 0
expr length test # 4
expr index test e # 2
Get first line:
head -n 1
Sleep for 1 second between each xargs command:
ps aux | awk '{print $1}' | xargs -I % sh -c '{ echo %; sleep 1; }'
Empty pagecache, dentries and inodes:
# run as root
# pagecache
free -h && echo && sync && echo 1 > /proc/sys/vm/drop_caches && free -h
# (not recomended) pagecache, dentries and inodes
free -h && echo && sync && echo 3 > /proc/sys/vm/drop_caches && free -h
Flush swap:
# run as root
swapoff -a && swapon -a
Command ‘ps’ options:
# show resource usage of process
ps -p <pid> -o %cpu,%mem,cmd,args # % - means without column header
Show count of processes of some user:
ps aux | awk '{print $1}' | grep <user> | wc -l
# show processes count of each user
ps -eo user=|sort|uniq -c
Show user group id’s (GID):
id <username>
Show free/usage space on partitions:
df -h # readable
-m
-k
Show count of chars, lines, bytes, etc.:
wc
Show size:
du <dir/file>
-h # readable
-s # size of dir
Show size and sort with hidden files/directories and total size:
du -sch /.[!.]* /* |sort -h
Show last lines of file in realtime:
tail -f <file>
Show listening ports:
netstat -antup
Change group:
chgrp [-R] <GID/gname>
Compress image size:
sudo apt-get install jpegoptim
# recursive compress with 50% quality
find . -type f -name "*.jpg" -exec jpegoptim -m50 {} \;
ARP:
arp # ARP table contains device addresses and mac's which located in same network
-n # only IP (without domains)
-a # IP and domains
# show in the file
cat /proc/net/arp
APT
apt-cache policy <package> # search versions of packages which enabled to install
fdisk -l # show info about disks and partitions
blkid # show small list of disks, UUID, TYPE
lsblk # show disk type, size, name, mountpoint
# show UUID of all disks
ls -al /dev/disk/by-uuid/
# show disk info
sudo hdparm -I /dev/sda
| grep -i trim # TRIM for SSD
# mount all from fstab (run it after fstab was changed)
sudo mount -a
# create partition table
sudo mkfs -t ext4 <device_name>
# create 100 files: file1, file2, ..., file100
touch file{1..100}
NMAP:
nmap <ip> # scan IP
-sT # TCP
-sU # UDP
-O # show software version
-v # show process of scannig
# show status of all services
service --status-all
Linux users and groups:
# add existing user to existing group
sudo usermod -a -G groupName userName
adduser <name> # create new user
-r # create system user
-g # group
useradd
-u # UID
-r # create system user
-g <group> # name or ID of group
-m # create home dir
-d <path> # path to home dir
-s <shell> # register shell for user
-c # comments
userdel <name> # delete user
-r # also delete home dir
# create group
groupadd <name>
-r # create system group
-g # group ID
Shutdown commands:
shutdown [options] now|<time> # power management
-r # reboot
-h # power off after shutdown
-c # cancelling scheduled shutdown
# poweroff now
shutdown -h now
halt -p
# send message to another user
write <user> [tty]
# show entered users
who
last # login history
reboot # reboot history
<user> # user login history
lastlog # show all user with login time
Show system information:
inxi -F # show information about system
lshw | more | less # show hardware information, also sector size
lscpu # show CPU information
# show hardware information, also type (virtual or bare metal)
sudo dmidecode -t system
CPU benchmark:
apt install sysbench
sysbench --test=cpu --cpu-max-prime=20000 run
Decrease *.vdi size:
# 1. On guest - zero fill free space
sudo dd if=/dev/zero of=zero bs=512k # bs=<sector size>
sudo rm zero
# 2. On host
vboxmanage modifyhd /path/to/thedisk.vdi --compact
# run command as another user
sudo -u lee <command>
# for adding PATH env
sudo nano /etc/environment
# restart networking
sudo ifconfig wlan0 down && sudo ifconfig wlan0 up
# get and show page
wget -qO- 127.0.0.1
grep:
grep -iR -E '(error_report|ini_set)' ./*.php # find in files
-R # recursive (include inherited dirs)
-l # show only file names
-i # ignore case sensetive
--exclude="*\.svn*" # exclude
--exclude-dir="dir" | {dir1,dir2} # exclude dir
-A <num> # show also <num> lines after
-B <num> # show also <num> lines before
Word replacement:
grep -Rl -E "(SOURCE)" ./* | xargs sed -i "s/SOURCE/DEST/g"
sed -i "s@SOURCE@DEST@g" /path/to/file
Remove the line which contains string:
# print the output to standard out
sed '/pattern to match/d' <file>
# directly modify the file (and create a backup). Will create <file>.bak.
sed -i.bak '/pattern to match/d' <file>
Replace whole line started by:
sed "s/start_of_line.*/new_line_content/g"
Find¶
find ./ -name 'path*'
-type (f=file, d=dir, l=link, p=pipe, s=socket)
find ./ -mtime 0 -type f -not -path "./" -exec cp --parents "{}" $TODAY_DIR/ \;
# chmod only files
find . -type f -exec chmod 644 {} \;
# faster chmod only files
find . -type f -print0 | xargs -0 chmod 644
# make iconv replace the input file with the converted output in one line
find . -type f -name '*.php' -exec sh -c 'iconv -f WINDOWS-1251 -t UTF-8 -o {}UTF_TMP {} && mv {}UTF_TMP {}' \;
# clear file
> filename
Delete old files¶
ls -t | sed -e '1,10d' | xargs -d '\n' rm -f
ls -t # lists all files in the current directory in decreasing order of modification time
sed -e '1,10d' # deletes the first 10 lines, ie, the 10 newest files
xargs -d '\n' rm # collects each input line (without the terminating newline) and passes each line as an argument to rm.
-f # ignore if empty
Create backup tar(tar.gz) archive:
tar -cvpzf backup.tar.gz [dir1] [dir2]
-c # create
-v # verbose mode
-p # preserving files and directory permissions.
-z # compress (tar.gz)
-f <filename>
--exclude=<file_or_dir>
Extract archive at current dir:
tar -xf <archive.tar.gz>
PASSWORD GENERATE:
apg
-t # print pronunciation for generated pronounceable passwor
-q # quiet mode (do not print warnings)
-n # count of generated passwords
-m # minimum pass length
-x # maximum pass length
-a # choose algorithm:
1 - random password generation according to password modes
0 - pronounceable password generation
# Example:
apg -q -m 8 -x 8 -a 1 -n 5
SECURITY¶
Find empty passwords:
awk -F: '($2 == "") {print}' /etc/shadow
Find users with uid == 0:
awk -F: '($3 == "0") {print}' /etc/passwd
Port listening check:
netstat -tulpn
Add service to autorun¶
Ubuntu 16.04:
sudo /bin/systemctl daemon-reload sudo /bin/systemctl enable <SERVICE_NAME>.service