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Wed, Jan 17, 2018 11:01 pm

Renewing a DHCP lease under OS X

If you wish to renew a Dynamic Host Configuration Protocol (DHCP) lease on a Mac OS X system, you can do so by clicking on the Apple icon in the upper, left-hand corner of the screen, selecting System Preferences, and then Network , and then the relevant network interface, e.g., Wi-Fi. Then click on the Advanced button and then the TCP/IP tab. You can then click on the Renew DHCP Lease button to have the system attempt to renew its DHCP lease.

[ More Info ]

[/os/os-x] permanent link

Tue, Jan 16, 2018 10:30 pm

Can't insert worksheet in Microsoft Excel for Mac 2016

When I tried to insert another worksheet in an Excel workbook today, I found that the option to insert a new blank worksheet was grayed out when I clicked on Insert and selected Sheet.

Excel 2016 - insert sheet grayed out

When I tried another means of adding a new sheet by clicking on the plus sign at the right side of the list of sheets in the worksheet to add the sheet, I saw an alert message stating "Workbook is protected and cannot be changed."

[ More Info ]

[/software/office] permanent link

Mon, Jan 15, 2018 7:37 pm

Using the Windows Resource Monitor to monitor network activity

If you want to see the IP addresses to which a program on a Microsoft Windows system is establishing connections, you can use the Resource Monitor utility that is provided with Windows Vista and later versions of Windows to check on network connections from a particular application on the system. To start the program, you can click on the Windows Start button and type resmon or resmon.exe in the "Search programs and files" field on a Windows 7 system or the "Type here to search" field on a Windows 10 system. You should see the resmon utility returned as the best match.

When the Resource Monitor program is running, you can click on the Network tab and then TCP Connections to see network activity associated with programs currently running on the system . You can click on a column header, e.g. "Image" to sort the entries by the values in that column.

[ More Info ]

[/os/windows/network/monitoring/resmon] permanent link

Sun, Jan 14, 2018 11:02 pm

Comodo OCSP

After I started the gVim text editor on a Windows laptop, I saw a "firewall alert" from the Symantec antivirus/firewall software on the system stating "Suspicious network activity has been detected." I've used gVim on many other systems for many years, but those systems weren't running the Symantec security software. The Symantec software showed that gvim.exe was attempting a Domain Name System (DNS) query to port 53, the well-known port for DNS, to IP address 8.8.8.8, the Google DNS server specified on the system for DNS queries.

[ More Info ]

[/network/ocsp] permanent link

Sat, Jan 13, 2018 10:20 pm

Using downloaded Visio stencils with Visio 2016

I needed to add a Juniper SRX Series Services Gateway to a network diagram created with Microsoft Visio 2016, so I downloaded the SRX Series stencils from Juniper Networks Product Icons & Visio Stencils page. The downloaded file was a ZIP file, so I extracted the contents of that file. Within the .zip file were two .VSS files: Juniper Branch SRX Series.vss and Juniper Data Center SRX Series.vss. On a Microsoft Windows system, if you wish to make shapes within a .vss file available within Visio, you can copy the .vss files to the My Shapes directory within the Documents directory for the account you are using. To then access the shapes, click on More Shapes on the left side of the Visio 2016 window, then select My Shapes. You should then see the names for the .vss files you added to the My Shapes directory listed.

[ More Info ]

[/os/windows/office/visio] permanent link

Fri, Jan 12, 2018 10:55 pm

Viewing only the files created today on a Linux system

I sometimes need to see only the files created or modified today in a directory. On a Linux system, you can pipe the output of the ls command into the grep command looking for just today's date in the input to the grep command as shown below:

$ ls -al --time-style=+%D ~/Documents/*.zip | grep $(date +%D)
-rw-r--r--. 1 joe joe   269338 01/12/18 /home/joe/Documents/gloves.zip
$

You can specify how the date is displayed with +format where format is a particular format in which you want the date displayed - see Formatting the output from the date command on a Linux system. If you use +%D, the date will be displayed as m/d/y, i.e., month/day/year, e.g. 01/12/18 for January 12, 2018. By then using the grep command to search for that value, you can limit the displayed files to only those created or modified today.

[ More Info ]

[/os/unix/commands] permanent link

Sat, Jan 06, 2018 5:01 pm

Configuring Sendmail to always allow Steam email

A family member wasn't receiving email for a Steam account she created to play a PC game. Her email comes through a Sendmail email server I manage and I found that a Domain Name System-based Blackhole List (DNSBL), the Spam and Open Relay Blocking System (SORBS), had blocked email from the IP address that Valve had for the email server used to send email to her about the account. When I checked the sendmail log file, I found the following two entries:

Dec 29 21:10:26 moonpoint sendmail[27413]: ruleset=check_relay, arg1=smtp03.stea
mpowered.com, arg2=127.0.0.6, relay=smtp03.steampowered.com [208.64.202.39], rej
ect=550 5.7.1 Spam Block:mail from 208.64.202.39 refused - see http://dnsbl.sorb
s.net/
Dec 29 21:17:35 moonpoint sendmail[27661]: ruleset=check_relay, arg1=smtp01.stea
mpowered.com, arg2=127.0.0.6, relay=smtp01.steampowered.com [208.64.202.37], rej
ect=550 5.7.1 Spam Block:mail from 208.64.202.37 refused - see http://dnsbl.sorb
s.net/

Checking, I found the following IP addresses and fully qualified domain names (FQDNs) for Steam email servers:

IP AddressFQDN
208.64.202.36 smtp.steampowered.com
208.64.202.37 smtp01.steampowered.com
208.64.202.38 smtp02.steampowered.com
208.64.202.39 smtp03.steampowered.com
208.64.202.40 steammail.steampowered.com

To ensure that none of the DNSBLs I use with Sendmail will ever block email from the Steam email servers, I added the following lines to /etc/mail/access:

Connect:208.64.202.36                           OK
Connect:208.64.202.37                           OK
Connect:208.64.202.38                           OK
Connect:208.64.202.39                           OK
Connect:208.64.202.40                           OK

I then used the makemap hash command to rebuild the access database.

# makemap hash /etc/mail/access </etc/mail/access
#

Once I did that, she was able to receive the Steam-related email.

[/network/email/sendmail] permanent link

Tue, Dec 12, 2017 11:25 pm

NetworkManager and nm-tool

If you wish to check the speed of network interfaces on a CentOS Linux system, if the nm-tool utility, is installed, then you can use it to determine the speed of the network ports.

$ nm-tool

NetworkManager Tool

State: disconnected

- Device: em1 ------------------------------------------------------------------
  Type:              Wired
  Driver:            bnx2
  State:             unmanaged
  Default:           no
  HW Address:        D4:AE:52:CD:0A:D4

  Capabilities:
    Carrier Detect:  yes
    Speed:           1000 Mb/s

  Wired Properties
    Carrier:         on


- Device: em2 ------------------------------------------------------------------
  Type:              Wired
  Driver:            bnx2
  State:             unmanaged
  Default:           no
  HW Address:        D4:AE:52:CD:0A:D5

  Capabilities:
    Carrier Detect:  yes

  Wired Properties
    Carrier:         off


$

If it is installed, the nm-tool program will likely be in /usr/bin . It is part of the NetworkManager package.

[ More Info ]

[/os/unix/linux/centos] permanent link

Sun, Dec 10, 2017 7:39 pm

Determining the version of CentOS on a system

If you are logged into a CentOS Linux system, there are a few ways you can determine the version of CentOS running on the system from a command-line interface (CLI), i.e., a shell prompt.

In the /etc directory, there should be a /etc/centos-release file containing information on the version of CentOS.

$ ls -l /etc/*elease
-rw-r--r--  1 root root  27 Mar 28  2017 /etc/centos-release
-rw-r--r--. 1 root root 152 Nov 25  2013 /etc/lsb-release
lrwxrwxrwx  1 root root  14 Apr 20  2017 /etc/redhat-release -> centos-release
lrwxrwxrwx  1 root root  14 Apr 20  2017 /etc/system-release -> centos-release
$ cat /etc/*elease
CentOS release 6.9 (Final)
LSB_VERSION=base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch:graphi
cs-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch
CentOS release 6.9 (Final)
CentOS release 6.9 (Final)
$

To just see the version number, you can use one of the grep commands below.

$ grep -oE '[0-9]+\.[0-9]+' /etc/redhat-release
6.9
$ grep -oE '[0-9]+\.[0-9]+' /etc/centos-release
6.9
$

[ More Info ]

[/os/unix/linux/centos] permanent link

Tue, Dec 05, 2017 10:53 pm

Determining if a site has implemented HTTP Strict Transport Security (HSTS)

HTTP Strict Transport Security (HSTS) is a security mechanism used by some websites to ensure that HTTP Secure (HTTPS) is always used by visitors to the site even should some intermediate system between the visitor's browser and the website attempt a man-in-the-middle (MITM) attack to downgrade the communications protocol to the unencrypted Hypertext Transfer Protocol (HTTP). The HSTS specification was published as Request for Comments (RFC) 6797 on November 19, 2012. You can tell whether a site has implemented HSTS by establishing a telnet connection to port 80, the well-known port for HTTP connections. E.g.:

$ telnet example.com 80
Trying 192.168.141.50...
Connected to example.com
Escape character is '^]'.
HEAD / HTTP/1.1
HOST: example.com

HTTP/1.1 301 Moved Permanently
Date: Wed, 06 Dec 2017 02:56:57 GMT
Server: Apache
X-Frame-Options: SAMEORIGIN
Strict-Transport-Security: max-age=31536000; includeSubDomains
Location: https://example.com/
Connection: close
Content-Type: text/html; charset=iso-8859-1

Connection closed by foreign host.
$

[ More Info ]

[/network/web] permanent link

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