Utils

css

Replace all occurrences of a string in a folder

ubuntu?

find /home/user/ -type f | xargs sed -i  's/a.example.com/b.example.com/g'

mac:

 LC_ALL=C find . -type f -name "*.html" -exec sed -i '' "s/UA-47088821-3/UA-47088821-4/" {} +

last 3 accessed files

 find . -type f -exec stat -c '%X %n' {} \; | sort -nr | awk 'NR==1,NR==3 {print $2}'

last 3 modified files

  find . -type f -exec stat -c '%Y %n' {} \; | sort -nr | awk 'NR==1,NR==3 {print $2}'

Find 10 largest files in a folder

 du -a /var | sort -n -r | head -n 10
 du -a .    | sort -n -r | head -n 15

For mac:

du -a . | sort -n -r | head

Limit how much logs journalctl keeps:

 journalctl --vacuum-time=2d
 journalctl --vacuum-size=500M

Count Lines in a Folder

find . -name "*js" -print | grep -v node_modules | xargs cat | grep -v "^//" | grep -v "^$" | wc -l

cut after ag for shorter lines

ag <your-search-keyword> | cut -c-800

increase number of open files, file descriptors

From: /etc/security/limits.conf

* - nofile 131072

*    soft nofile 64000
*    hard nofile 64000
root soft nofile 64000
root hard nofile 64000

Reload services after making changes, logout.

count open files

lsof | wc -

Per user:

lsof | grep ' opera ' | awk '{print $NF}' | sort | wc -l

Set date

sudo date --set "25 Sep 2013 15:00:00"

Get date in milliseconds

date -d 2017-05-05 +%s

Disks, Storage

check disks on ubuntu

 sudo lsblk

Mount a block device

From: https://www.digitalocean.com/community/tutorials/how-to-use-block-storage-on-digitalocean

 parted /dev/sda mklabel gpt
 parted -a opt /dev/sda mkpart primary ext4 0% 100% 
 mkfs.ext4 /dev/sda
 mkdir -p /data
 '/dev/sda /data ext4 defaults,nofail,discard 0 2' | sudo tee -a /etc/fstab
 mount -a

Find large files

find / -xdev -type f -size +100M

see timestamps in history

echo 'export HISTTIMEFORMAT="%d/%m/%y %T "' >> ~/.bashrc ; source ~/.bashrc

Generate large random file

dd if=/dev/urandom of=/var/log/mongodb/randomFile bs=1M count=200

Add ssh key to a server

cat ~/.ssh/id_rsa.pub | ssh user@hostname 'cat >> .ssh/authorized_keys'

Add identity to a server

ssh-copy-id -i ~.ssh/key_name.pub user@host

Create a user

su - <username>
sudo visudo -f /etc/sudoers
usernameusedforlogin ALL=(ALL) NOPASSWD:ALL
sudo adduser --disabled-password <username>

add user to group:

usermod -a -G wheel niceguy
useradd -g wheel niceguy ## only is user doesn't exist!

or in rhel:

passwd -f -u deploy
(and there is deluser)
(I don't think I need this: usermod -aG sudo username ) - for making him a sudoer

useradd? adduser?

adduser : add user with full profile and info (pass, quota, permission, etc.) adduser is friendlier in that it sets up the account's home folders and other settings (e.g. automatically loading system stats and notifications on login),

whereas useradd just creates the user

Establish a simple ssh port forward

10.0.0.x is public, 10.0.1.x is private. Do:

sudo sysctl net.ipv4.ip_forward=1
sudo iptables -t nat -A PREROUTING -p tcp -d 10.0.0.229 --dport 2270 -j DNAT --to-destination 10.0.1.224:22
sudo iptables -t nat -A POSTROUTING -j MASQUERADE

Delete files older than 5 days

find /path/to/files* -mtime +5 -exec rm {} \;
find /path/to/files* -type f -mtime +5 -exec rm {} -v \;

get children of a process

pgrep -P $your_process1_pid

restrict resources given to a process

sudo apt-get install cgroup-bin -y
sudo cgcreate -g memory:/rmGroup
sudo
 echo $(( 500 * 1024 * 1024 )) > /sys/fs/cgroup/memory/rmGroup/memory.limit_in_bytes
 # echo $(( 5000 * 1024 * 1024 )) > /sys/fs/cgroup/memory/rmGroup/memory.memsw.limit_in_bytes # swap only
# cgexec -g memory:rmGroup <command>
cgexec -g memory:rmGroup find cache/ -type f -mtime +10 -exec rm {} -v \;

Linux utils

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