Tips & Tricks

Create a limited user

sudo adduser limiteduser --shell=/bin/false --no-create-home

Add below lines in /etc/ssh/sshd_config

Match user limiteduser
   ForceCommand /bin/false

Resize the partition

apk add --no-cache e2fsprogs-extra

resize2fs /dev/mmcblk0p2

The partition will be resized to maximum size

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iptables and ip6tables

List:

iptables -t nat -v -L -n --line-number

ip6tables -t nat -v -L -n --line-number

Delete rule:

 iptables -t nat -D POSTROUTING 2

 ip6tables -t nat -D POSTROUTING 2

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Alpine IMAGES

Backup the 2 partitions from SD card to .img files

 dd bs=4M if=/dev/sdb1 of=Alpine_sdb1.img

 dd bs=4M if=/dev/sdb2 of=Alpine_sdb2.img

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Write the .img files to a new SD card, formatted with 2 partitions: sdb1=FAT32, 400 MB, and sdb2=ext4, the rest of the card

   dd if=Alpine_sdb1.img of=/dev/sdb1 bs=4M

   dd if=Alpine_sdb2.img of=/dev/sdb2 bs=4M

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Grep

grep -v '^#' hostapd.conf  

• print file without lines starting with #

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SSH

rm -rf /root/.ssh

rm -rf /home/iblocker/.ssh/

rm -rf /var/www/.ssh/

ssh-keygen -t rsa -q -f "/root/.ssh/id_rsa" -N ""

cp /root/.ssh/id_rsa.pub /root/.ssh/authorized_keys

ssh -o StrictHostKeyChecking=no root@localhost "exit"

cp /root/.ssh /var/www -R

cp /root/.ssh /home/iblocker -R

chown iblocker:iblocker /home/iblocker/.ssh -R

chmod 755  /var/www/.ssh/

chmod 755  /var/www/.ssh/*

chown apache:apache /var/www/.ssh -R

chown root:root /var/www/.ssh/*

chmod 755  /var/www/.ssh/*

ssh-keyscan -H localhost  >> /var/www/.ssh/known_hosts

Check: ssh root@localhost

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Enable Auth Log

apk add --no-cache syslog-ng

Add below lines at the end of /etc/syslog-ng/syslog-ng.conf

filter f_auth { facility(auth); };
log { source(src); filter(f_auth); destination(auth_log); };

Change permissions and restart the service:

chmod 640 /var/log/auth.log
rc-service syslog restart

Verify log: tail -f /var/log/auth.log

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DNS ISSUE - "request is not signed"

Solution:

systemctl stop named.service

rm -r /var/cache/bind/*

systemctl start named.service

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SET TIME

date --set="2024-08-14 10:07:00"

Wed Aug 14 10:07:00 CEST 2024

hwclock --systz

In case time is de-synchronized, comment out the below line from /etc/conf.d/syslog:

SYSLOGD_OPTS="-t"

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Disable service

 rc-update del acpid

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Enable service

apk add dhcpcd  - for IPv6 on eth0 or usb0

rc-update add dhcpcd

rc-service  dhcpcd start

rc-status

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SED

sed -E '/(^$|^#)/d' input.file > input1.file  

• delete lines containing # as first character and empty lines

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ffmpeg

Convert .avi to .mp4

 ffmpeg -i single-cam.avi -c:v libx264 -crf 18 -c:a aac -b:a 128k single-cam.mp4

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