Linux Tips and Tricks (Ubuntu, Debian)

倾城 • 2025-11-02 13:51 • 好物分享

This post is to summarize some interesting but special usage which is out of normal linux commands. For basic Linux commands, you can find it from my previous post.

Convert NTFS to EXT4 in Linux

systemctl stop nfs-kernel-server

docker stop filebrowser

root@pi:/mnt/usb1/data# fuser -v /mnt/usb1

USER PID ACCESS COMMAND

/mnt/usb1: root kernel mount /mnt/usb1

fuser -km /mnt/usb1

umount /mnt/usb1

root@pi:~# ntfsresize --no-action /dev/sda1 -f

ntfsresize v2022.10.3 (libntfs-3g)

Device name : /dev/sda1

NTFS volume version: 3.1

Cluster size : 4096 bytes

Current volume size: 1000202273280 bytes (1000203 MB)

Current device size: 1000202273280 bytes (1000203 MB)

New volume size : 1000202273280 bytes (1000203 MB)

Nothing to do: NTFS volume size is already OK.

ntfsresize --size 200G /dev/sda1 -f

After resize ntfs, you can create a new partition with ext4 format, then copy data from ntfs to ext4 partition. Once done data transfer, delete ntfs partition and expant ext4 partition.

Format the disk (or partition) to ext4
To format the whole disk or a partition, use the following command:
```
text
sudo mkfs.ext4 /dev/sdX1 
```
Replace /dev/sdX1 with your USB disk partition. If your disk has multiple partitions and you want to format the entire disk, consider creating a new partition table first and then formatting the partition you create.

root@pi:~# mkfs.ext4 /dev/sda1 mke2fs 1.47.0 (5-Feb-2023) /dev/sda1 contains a ntfs file system labelled '1T' Proceed anyway? (y,N) y Creating filesystem with 244190008 4k blocks and 61054976 inodes Filesystem UUID: 432f2c49-5a45-42ca-9138-6b576c7c5ddd Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424, 20480000, 23887872, 71663616, 78675968, 102400000, 214990848 Allocating group tables: done Writing inode tables: done Creating journal (262144 blocks): done Writing superblocks and filesystem accounting information: done

Read / Write Disk Performance Test

Using `dd` for Disk Read Testing

Write a test file (if you don't already have one):


text
dd if=/dev/zero of=/tmp/testfile bs=1M count=1024 conv=fdatasync

This writes a 1GB file to /tmp/testfile with conv=fdatasync ensuring data is physically written to disk.

Clear the Linux buffer cache to avoid reading from memory cache:


text
sudo sh -c "echo 3 > /proc/sys/vm/drop_caches"

Run the read test by reading the file to /dev/null:


text
dd if=/tmp/testfile of=/dev/null bs=1M count=1024

This reads the 1GB test file and discards the output, measuring the read throughput from disk.

For my external usb disk mounted on Raspberry Pi 2B with ntfs format:

root@pi:~# dd if=/dev/zero of=/mnt/usb1/data/testfile bs=1M count=1024 conv=fdatasync 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB, 1.0 GiB) copied, 135.585 s, 7.9 MB/s root@pi:~# dd if=/mnt/usb1/data/testfile of=/dev/null bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB, 1.0 GiB) copied, 42.2893 s, 25.4 MB/s root@pi:~#

I got 7.9MB/s write speed and 25.4 MB/s read speed for ntfs partition.

For ext4 format:

root@pi:/mnt/usb1# dd if=/dev/zero of=/mnt/usb1/testfile bs=1M count=1024 conv=fdatasync 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB, 1.0 GiB) copied, 39.3389 s, 27.3 MB/s root@pi:/mnt/usb1# dd if=/mnt/usb1/testfile of=/dev/null bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB, 1.0 GiB) copied, 41.8176 s, 25.7 MB/s root@pi:/mnt/usb1#

I got 27.3MB/s write speed and 25.7 MB/s read speed for ext4 partition. Much faster on write speed.

Ubuntu CLI Cheat Sheet

Ubuntu Pro

This will get rid of most of your security vulnerability scan findings.

https://ubuntu.com/pro/tutorial

Commands:

pro --version
sudo apt install ubuntu-advantage-tools
pro security-status
pro security-status --help
pro help esm-apps

Get your Ubuntu registered into your Pro subscription

sudo pro attach [YOUR_TOKEN]

To ensure that all available CVE fixes are applied, run:

 $ sudo apt update && sudo apt upgrade

Configure DNS Server for your Linux

You can use either /etc/resolve.conf or netplan to set up your dns server. But netplan will take into effct first.

1. Check current dns server in /etc/resolv.conf

nslookup

> server

Default server: 127.0.0.53

Address: 127.0.0.53#53

2. Modify DNS server

nano /etc/resolve.conf

On Ubuntu 24.04, the DNS server specified in the netplan configuration (such as

1.1.1.1

) will be the one in effect, not the DNS listed in /etc/resolv.conf (such as

8.8.8.8

DNS Resolution Flow

Netplan sets DNS servers via YAML files, which are then picked up by the system's network renderer (NetworkManager, systemd-networkd, etc.), configuring systemd-resolved as the authoritative source for DNS settings.
/etc/resolv.conf is commonly a symbolic link automatically managed by systemd-resolved and overwritten on boot or after networking changes.
Manual changes to /etc/resolv.conf are temporary and will be overridden by what is set in Netplan or systemd-resolved configurations.

Which DNS Will Be Used?

If netplan has DNS configured (such as1.1.1.1 ), it will instruct systemd-resolved to use it, and systemd-resolved will manage and update /etc/resolv.conf accordingly.
The DNS that is actually queried by applications will be the one provided via netplan (and thereby systemd-resolved), not whatever has been manually set in /etc/resolv.conf.
To see the effective DNS server, use:

On Ubuntu 24.04 use following command:

resolvectl status

Or in other version or release, you can use this command:

systemd-resolve --status

Summary Table

Configuration File	Effect on DNS	Persistence
Netplan (.yaml)	Takes effect	Permanent
/etc/resolv.conf (manual edit)	Overwritten/ignored	Temporary/unreliable

List All Running Services

systemctl --type=service --state=running

Add user into sudo / wheel

adduser newuser

passwd newuser

On Ubuntu:

usermod -aG sudo newuser

On CentOS:

usermod -aG wheel newuser

Manually Change IP

Ubuntu:

Before version 17.10, edit file /etc/network/interfaces
Starting with 17.10, Netplan is the default network management tool

ip link
nano /etc/netplan/01-netcfg.yaml
netplan apply

CentOS

“nmcli d” command in your terminal for quick list ethernet card installed on your machine:
“nmtui” command in your terminal to open Network manager.

IPv4 configuration <Automatic>
[x] Automatically connect
service network restart
ip a

There are more ways to configure static ip on Raspberry PI:

https://blog.51sec.org/2020/04/install-ubuntu-2004-on-raspberry-pi.html

Check Your Public IP Address from CLI

Following commands can show you what the public ip address is for your linux machine if it can connect to Internet.

curl -s
checkip.dyndns.org

|sed -e 's/.*Current IP Address: //' -e 's/<.*$//'
curl
icanhazip.com
curl http://
ipv4.icanhazip.com
telnet
www.checkmyip.com

80 | grep confidence | grep -Eo '([0-9]{1,3}/.){3}[0-9]{1,3}'
wget -O - -q
icanhazip.com
wget http://
ipinfo.io

/ip -qO -
curl
ifconfig.me
curl ip.sb

Keep Terminal Running in background (Screen)

Install screen (Depends on the Linux Distribution if it came pre installed or not) : yum install screen . Or in Debian based OS, such as Ubuntu: apt install screen
Initiate a Screen : screen or screen -S <screen name> <command to execute>
Detach from the screen : "CTRL+A,D" not "CTRL+A+D"
List all the screen currently working : screen -ls
Reattach to a screen : screen -r <session number> or screen -r <screen name>
Kill specific screen: screen -X -S <screen name> quit
Kill all screens : pkill screen

To list available sessions and their IDs:

Code

 screen -ls

Name a screen session.

Code

 screen -S <session_name>

This allows reattaching using the name:

Code

 screen -r <session_name>

Log into Linux Using Self-Created SSH Key From Windows

1. Generate SSH Key in PowerShell

Open PowerShell and run:

ssh-keygen -t rsa -b 4096

2. Transfer Public Key to Linux

type $env:USERPROFILE/.ssh/id_rsa.pub | ssh username@linux-host "mkdir -p .ssh && chmod 700 .ssh && cat >> .ssh/authorized_keys && chmod 600 .ssh/authorized_keys"

Replace username and linux-host with your Linux user and IP/hostname

Alternatively, manually copy the contents of id_rsa.pub and paste into the Linux server’s .ssh/authorized_keys file, ensuring correct file permissions (chmod 600 ~/.ssh/authorized_keys).

Or To transfer a self-created SSH public key from Windows to Linux and append it to ~/.ssh/authorized_keys for passwordless SSH login, use SCP to copy the key, then SSH to append it with a one-liner:

scp C:/Users/<WindowsUser>/.ssh/id_rsa.pub username@linux-host:~/id_rsa.pub; ssh username@linux-host "mkdir -p ~/.ssh && chmod 700 ~/.ssh && cat ~/id_rsa.pub >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys && rm ~/id_rsa.pub

Note" If you can make sure authorized_keys is empty, you can use this command to copy the key over

scp C:/users/netsec/.ssh/id_ed25519.pub [email protected]:/root/.ssh/authorized_keys

3. Test Passwordless SSH Login

ssh username@linux-host

Build SSH Trust Relationship Between Linux Machines

Become root:

sudo su -

Change to user nsm:
su nsm

Go to the /home/nsm directory:
cd /home/nsm

Create the keys: (Path should be /home/nsm/.ssh/id_rsa. Leave the passphrase blank.)

ssh-keygen -t rsa

Secure copy the public key to the other server as the admin user: (use admin password)

scp /home/nsm/.ssh/id_

rsa.pub

admin@<ipAddressOfOtherServer>:/home/admin/authorized_keys

or Go to the remote server. The command below will add the key that is in temp1 file to the end of the authorized_keys file.

cat temp1 >> authorized_keys

Repeat steps 2-6 on deviceB. On deviceB, become root: (from user nsm, exit to root). Move the authorized_keys file that was copied to admin into nsm/.ssh:

mv /home/admin/authorized_keys /home/nsm/.ssh/authorized_keys

Change ownership of authorized_keys:

chown nsm:nsm /home/nsm/.ssh/authorized_keys

At this point, you will be able to SSH between both servers without it asking for a password.

ssh [email protected]

Find Large Folders

1. Use NCDU program to check folder size.

2. Check your application

For example: pihole folder, pihole-FTL.db, which holds long term query data. It can get quite large with years usage.

/root/etc-pihole/pihole-FTL.db

3. Check /var/log/journalctl

You can diminish the size of the journal by means of these commands:

sudo journalctl --vacuum-size=100M

This will retain the most recent 100M of data.

sudo journalctl --vacuum-time=10d

will delete everything but the last 10 days.

Find Big Files in Linux File System

Check folders size Command - DU :

bitnami@ip-172-26-0-136:/opt$ du -shc /opt/bitnami/apps/wordpress/htdocs/wp-content/* 1.8G /opt/bitnami/apps/wordpress/htdocs/wp-content/ai1wm-backups 24K /opt/bitnami/apps/wordpress/htdocs/wp-content/backup-migration 4.0K /opt/bitnami/apps/wordpress/htdocs/wp-content/blogs.dir 24K /opt/bitnami/apps/wordpress/htdocs/wp-content/cache 4.0K /opt/bitnami/apps/wordpress/htdocs/wp-content/index.php 6.3M /opt/bitnami/apps/wordpress/htdocs/wp-content/languages 132M /opt/bitnami/apps/wordpress/htdocs/wp-content/plugins 27M /opt/bitnami/apps/wordpress/htdocs/wp-content/themes 152K /opt/bitnami/apps/wordpress/htdocs/wp-content/updraft 4.0K /opt/bitnami/apps/wordpress/htdocs/wp-content/upgrade 512M /opt/bitnami/apps/wordpress/htdocs/wp-content/uploads 68K /opt/bitnami/apps/wordpress/htdocs/wp-content/w3tc-config 2.4G total

Find Command:

find . -type f -size +10000 -exec ls -lh {} /;
find . -type f -size +50000k -exec ls -lh {} /; | awk '{ print $9 ": " $5 }'
Find large files (>10M) in current folder

find . -type f -size +10000k

a. Juniper Firewall

Sample output:

root@FW% find . -type f -size +10000 -exec ls -lh {} /;
-rw-r--r-- 1 930 929 134M Jan 5 17:34 ./cf/packages/junos-11.4R6.6-domestic
-rw-r--r-- 1 root wheel 139M Sep 8 2011 ./cf/var/log/junos-srxsme-11.2R2.4-domestic.tgz
-rw-r----- 1 root wheel 4.9M Feb 11 17:12 ./cf/var/db/idpd/db/secdb_02.db
-rw-r----- 1 root wheel 6.7M Feb 11 17:13 ./cf/var/db/idpd/db/secdb_03.db
-rw-r----- 1 root wheel 64M Feb 11 17:13 ./cf/var/db/idpd/db/secdb_06.db
-rwxr-xr-x 1 admin 20 24M May 23 08:38 ./cf/var/db/idpd/nsm-download/SignatureUpdate.xml
.....

b. Checkpoint Firewall gateway:

[Expert@CP]# find . -type f -size +50000k -exec ls -lh {} /; | awk '{ print $9 ": " $5 }'
./sysimg/CPwrapper/linux/CPEndpointSecurity/EndpointSecurityServer.bin: 145M
./sysimg/CPwrapper/linux/windows/SmartConsole.exe: 194M
./sysimg/CPwrapper/linux/CPrt/CPrt-R75.40-00.i386.rpm: 53M
./sysimg/CPwrapper/linux/CPportal/CPportal-R75.40-00.i386.rpm: 59M
./var/log/db: 336M
....

Some other commands to help you find out which folder or files using your space:

df -h //check disk usage du -sh /* | sort -nr // check each folder's usage du -sh /var/* | sort -nr //check internal folder usage inside folder /var du -h --max-depth=1 lsof | grep deleted //check if there is deleted file locked by process. cat /dev/null > filename //clear up logs rm -rf filename //clean up /var/log/journal files journalctl --vacuum-time=1w //keep one week log journalctl --vacuum-size=500M //keep only 500MB logs rm -rf /var/log/journal/f9d400c5e1e8c3a8209e990d887d4ac1
 //delete /var/log/journal log files

Clean all Linux History

1. Clear systemd journal logs

It will delete archived journal log files until usage is less 100MB

sudo journalctl --rotate --vacuum-size=100M

2. Clear history trails

Following commands can clean most of your history trails in your linux system. Please let me know if you found there is anything missing. I will add the command in.

echo > /var/log/wtmp echo > /var/log/btmp echo >/var/log/lastlog echo > /var/log/secure echo > /var/log/messages echo >/var/log/syslog echo >/var/log/xferlog echo >/var/log/auth.log echo >/var/log/user.log cat /dev/null > /var/adm/sylog cat /dev/null > /var/log/maillog cat /dev/null > /var/log/openwebmail.log cat /dev/null > /var/log/mail.info
 echo >/var/run/utmp echo > ~/.bash_history history -c echo > .bash_history history -cw

3. To Clean all log files

For CentOS 6:

cat /dev/null > /var/log/boot.log cat /dev/null > /var/log/btmp cat /dev/null > /var/log/cron cat /dev/null > /var/log/dmesg cat /dev/null > /var/log/dracut.log cat /dev/null > /var/log/lastlog cat /dev/null > /var/log/maillog cat /dev/null > /var/log/messages cat /dev/null > /var/log/secure cat /dev/null > /var/log/spooler cat /dev/null > /var/log/tallylog cat /dev/null > /var/log/wtmp cat /dev/null > /var/log/yum.log

For CentOS 7:

cat /dev/null > /var/log/boot.log cat /dev/null > /var/log/btmp cat /dev/null > /var/log/cron cat /dev/null > /var/log/dmesg cat /dev/null > /var/log/firewalld cat /dev/null > /var/log/grubby cat /dev/null > /var/log/lastlog cat /dev/null > /var/log/mail.info
 cat /dev/null > /var/log/maillog cat /dev/null > /var/log/messages cat /dev/null > /var/log/secure cat /dev/null > /var/log/spooler cat /dev/null > /var/log/syslog cat /dev/null > /var/log/tallylog cat /dev/null > /var/log/wpa_supplicant.log cat /dev/null > /var/log/wtmp cat /dev/null > /var/log/yum.log

Use ssh key to encrypt / decrypt files

Create a file:
echo ‘This is a sekret’ >/tmp/msg.txt

Export public key:
openssl rsa -in ~/private.pem -out /tmp/

public.pub

-outform PEM -pubout

Encrypt file with public key (anyone can have this key):
openssl rsautl -encrypt -inkey /tmp/

public.pub

-pubin -in /tmp/msg.txt -out /tmp/file.enc

Decrypt the file with private key (only you should have the private key):
openssl rsautl -decrypt -inkey ~/private.pem -in /tmp/file.enc -out /tmp/decrypted.txt

Check decoded message:
cat /tmp/decrypted.txt

AWS Amazon Linux Instance Commands

sudo yum update -y
sudo yum install -y httpd24 php70 mysql56-server php70-mysqlnd
sudo service httpd star

sudo chkconfig httpd on
chkconfig --list httpd
curl http://localhost

sudo usermod -a -G apache ec2-user
groups
sudo chown -R ec2-user:apache /var/www
sudo chmod 2775 /var/www
find /var/www -type d -exec sudo chmod 2775 {} /;
find /var/www -type f -exec sudo chmod 0664 {} /;
echo "<?php phpinfo(); ?>" > /var/www/html/phpinfo.php
sudo yum list installed httpd24 php70 mysql56-server php70-mysqlnd
sudo service mysqld start
sudo chkconfig mysqld on
sudo service httpd restart

Validate UDP ports reachability

Ensure, that your ports are reachable through your external IP.
To validate UDP connection the simplest way, run this on your server:

nc -ul 52101

And this on your local client:

nc -u [server ip] 52101

Then try to type on one end, you should see characters on the other side.
If it does not work for you, then most likely your port forwarding is not working correctly. Or your ISP is blocking traffic.

If you get Command 'nc' not found. error, you can install netcat package using:

sudo apt-get install netcat

Check Logs

Check a service logs (-f, --follow: show only the most recent journal entries, and continuously print new entries as they are appended to the journal.):

journalctl -u cloudflared -f

Or using tail command:cd ..

tail -f /tmp/myapp.log /var/log/postgresql/postgresql.main.log <(journalctl -f)

journalctl -xe

版权声明：
作者：倾城
链接：https://www.techfm.club/p/226070.html
来源：TechFM
文章版权归作者所有，未经允许请勿转载。

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Linux Tips and Tricks (Ubuntu, Debian)

Convert NTFS to EXT4 in Linux

Read / Write Disk Performance Test

Using `dd` for Disk Read Testing

Ubuntu CLI Cheat Sheet

Ubuntu Pro

Configure DNS Server for your Linux

1. Check current dns server in /etc/resolv.conf

2. Modify DNS server

DNS Resolution Flow

Which DNS Will Be Used?

Summary Table

List All Running Services

Add user into sudo / wheel

Manually Change IP

Check Your Public IP Address from CLI

Keep Terminal Running in background (Screen)

Log into Linux Using Self-Created SSH Key From Windows

Build SSH Trust Relationship Between Linux Machines

Find Large Folders

Find Big Files in Linux File System

a. Juniper Firewall

b. Checkpoint Firewall gateway:

Clean all Linux History

Use ssh key to encrypt / decrypt files

AWS Amazon Linux Instance Commands

Validate UDP ports reachability

Check Logs

取消回复

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Linux Tips and Tricks (Ubuntu, Debian)

Convert NTFS to EXT4 in Linux

Read / Write Disk Performance Test

Using dd for Disk Read Testing

Ubuntu CLI Cheat Sheet

Ubuntu Pro

Configure DNS Server for your Linux

1. Check current dns server in /etc/resolv.conf

2. Modify DNS server

DNS Resolution Flow

Which DNS Will Be Used?

Summary Table

List All Running Services

Add user into sudo / wheel

Manually Change IP

Check Your Public IP Address from CLI

Keep Terminal Running in background (Screen)

Log into Linux Using Self-Created SSH Key From Windows

Build SSH Trust Relationship Between Linux Machines

Find Large Folders

Find Big Files in Linux File System

a. Juniper Firewall

b. Checkpoint Firewall gateway:

Clean all Linux History

Use ssh key to encrypt / decrypt files

AWS Amazon Linux Instance Commands

Validate UDP ports reachability

Check Logs

取消回复

共有 0 条评论

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Using `dd` for Disk Read Testing