How to find process listening over a port

List all tcp ports using netstat -at

netstat -at
 netstat -ltnp 

-p means list all the programs run over the port

List all udp ports using netstat -au

netstat -aup

List only listening ports using netstat -l

netstat -lp

List only the listening UNIX Ports using netstat -lx

netstat -lxp

lsof command (LiSt Open Files) is used to list all open files on a Linux system. To install it on your system, type the command below.

$ sudo yum install lsof	        #RHEL/CentOS 
$ sudo apt install lsof		#Debian/Ubuntu
$ sudo dnf install lsof		#Fedora 22+

To find the process/service listening on a particular port, type (specify the port).

$ lsof -i :80

Create bootable USB stick from ISO in Mac OS X

Convert the ISO to UDRW format

Mac OS X provides all the tools needed to convert the ISO image to UDRW. The following command will convert the ISO image to the UDRW format.

hdiutil convert -format UDRW -o destination_file.img source_file.iso

You will notice that the destination_file.img from the command will create the file destination_file.img.dmg really. This is because the hdiutil program automatically adds the dmg file extension. This is not a problem as the file extension won’t affect the format of the image.

Prepare the USB stick

Check your USB stick and make a backup if there is any important data on it, as the next steps are going to delete everything on it.

To prepare the USb stick we are going to delete all the partitions on the stick and create an empty partition. To do this we need to know the device name of the USB stick. Open a terminal and execute the following command:

$ diskutil list

You will see a list of disks and partitions. The goal is to identify the USB stick in this output. Depending on your system configuration your output might look different from this one. This appears to show 3 physical discs but it does not. The /dev/disk1 is a virtual disk created because of the partition encryption (FileVault 2) I enabled in Mac OS X.

#:                       TYPE NAME                    SIZE       IDENTIFIER
0:      GUID_partition_scheme                        *500.1 GB   disk0
1:                        EFI                         209.7 MB   disk0s1
2:          Apple_CoreStorage                         399.5 GB   disk0s2
3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
5:                 Apple_Boot Boot OS X               134.2 MB   disk0s5
#:                       TYPE NAME                    SIZE       IDENTIFIER
0:                  Apple_HFS MacOSX                 *399.2 GB   disk1
#:                       TYPE NAME                    SIZE       IDENTIFIER
0:      GUID_partition_scheme                        *2.0 GB     disk2
1:       Microsoft Basic Data UNTITLED 1              2.0 GB     disk2s1

As shown in the output above, the connected USB stick is a small 2.0 GB drive with a FAT partition on it. We are now going to remove this partition in the next step. For the following steps we will need the name of the disk which in this case is “/dev/disk2”.

With the following command the data on the disk (your USB stick) will be deleted!

$ diskutil partitionDisk /dev/disk2 1 "Free Space" "unused" "100%"

With this command the USB stick was re-partitioned to have 1 partition without formatting and 100% of the size of the stick. If you check it again with “diskutil list” you will see the changes already, also the USB stick will no longer be shown in the Finder.

Copy the image to the USB stick

Now we can copy the disk image we created to the USB stick. This is done via the dd(1)command. This command will copy the image to the disk (substitute the appropriate disk name for your USB stick here, as with the re-partitioning command):

$ sudo dd if=destination_file.img.dmg of=/dev/disk2 bs=1m

The dd command does not show any output before it has finished the copy process, so be patient and wait for it to complete.

$ diskutil eject /dev/disk2

To eject the USB stick, use the above command. After this is done, the bootable USB stick is ready to be used.

Original link

GitLab set up ssh key

From local command console type:

cat ~/.ssh/

If you see a string starting with ssh-rsa you already have an SSH key pair otherwise you have to generate it.

EX: ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAAAgQC8PAgJVXMQysVOuI0znKGXaUNqdk4reejNPKlG+/RZ+B47YWmiL/qIFx6ILjLQa8iRMmAj9n3hRGBQoIQnU0ZzickuQ/AJi4cEr2+4Hm6I3QTqodWGOijRBXjhGoToIGAAu1ymM+zNSMMtBvMhaOl8QUFY4dAb6YyZs/gvnWKczw== [email protected]

in the user profile add a ssh public key

Don’t paste the private part of the SSH key. Paste the public part, which is usually contained in the file ‘~/.ssh/’ and begins with ‘ssh-rsa’


Error: modseq_hdr.log_offset too large Centos 7

2018-01-02 01:40:59 imap([email protected]): Fatal: master: service(imap): child 18780 killed with signal 6 (core dumps disabled)

2018-01-02 01:40:59 imap([email protected]): Error: /var/vmail/ modseq_hdr.log_offset too large

2018-01-02 01:40:59 imap([email protected]): Error: /var/vmail/ modseq_hdr.log_offset too large

2018-01-02 01:40:59 imap([email protected]): Panic: file mail-transaction-log-file.c: line 1148 (mail_transaction_log_file_get_highest_modseq_at): assertion fa

iled: (offset <= file->sync_offset)


find /var/vmail/ -name "dovecot*" -delete


Restart Postfix & Dovecot (to rebuild the dovecot files):

$ service dovecot restart
$ service postfix restart

I think the cause is the presence of a virus in some emails attachment.

thanks to this link