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Sat, Aug 27, 2016 10:39 pm

Obtaining a list of fonts on a Mac OS X system

You can obtain a list of the fonts on a Mac OS X system using the system_profiler command system_profiler SPFontsDataTye. A large amount of information will be displayed for each font, so you may want to capture the output in a file, e.g. fontslist.txt.
$ system_profiler SPFontsDataType > fontslist.txt

If you want the output in XML format, you can include the -xml option, e.g. system_profiler -xml SPFontsDataType > fontslist.xml.

[ More Info ]

[/os/os-x] permanent link

Fri, Aug 26, 2016 9:39 pm

Unpausing paused OS X applications

I had a lot of windows and tabs open in the Safari web browser on my MacBook Pro laptop running OS X 10.10.5 (Yosemite) as well as many other apps open. I've found when I leave many browser tabs open for a prolonged period that eventually they consume almost all of the system's memory. The Activity Monitor application was showing about 15 GB of the system's 16 GB of memory as in use. I closed a couple of tabs, but then opened another one. Then I got the "spinning beachball" and could do nothing further with Safari, so I clicked on the Apple icon at the top, left-hand corner of the screen and chose Force Quit and forced Safari to quit. That reduced the "memory used" value from about 15 GB down to about 5 GB, but I saw that many other applications were listed as "paused" in the Force Quit Applications window and I could no longer use those applications - I just got the multi-colored, spinning beach ball when I clicked on them or tried to access them by cycling through open applications with Command-Tab.

Force Quit Applications - 
apps paused

The Activity Monitor window showed those applications as "Not Responding".

Activity Monitor - Not Responding

The Terminal application is not shown as "Not Responding" in the Activity Monitor window, though it is shown as "paused" in Force Quit Applications because I unpaused it prior to taking the Activity Monitor screenshot. To unpause applications, I needed to access a Terminal window to issue "kill -CONT" commands. You can use kill commands to stop errant processes, but you can also use kill -CONT pid commands where pid is the process identifier (PID) of the process you wish to "unpause" to cause a process to resume or "continue" its operation - see Suspending and resuming a process on OS X.

[ More Info ]

[/os/os-x] permanent link

Thu, Aug 25, 2016 10:32 pm

cat, rev, and tac commands

If you want to display the contents of a file on a Linux system, you can use the cat command - the "cat" is shorthand for "concatenate.

 $ cat sample.txt
Adhere to your purpose and you will soon feel as well as you ever did.
On the contrary, if you falter, and give up,
you will lose the power of keeping any resolution,
and will regret it all your life.
~ Abraham Lincoln in a June 28, 1862 letter to Quintin Campbell
$

Should you ever need to display the characters on a line in reverse order, on a Linux system you can use the rev command to do so - the "rev" is shorthand for "reverse". E.g., suppose I want to display the same file as in the example above. If I type rev sample.txt, I will see every line displayed in reverse with the last character in the line becoming the first and the first the last.

$ rev sample.txt
.did reve uoy sa llew sa leef noos lliw uoy dna esoprup ruoy ot erehdA
,pu evig dna ,retlaf uoy fi ,yrartnoc eht nO
,noituloser yna gnipeek fo rewop eht esol lliw uoy
.efil ruoy lla ti terger lliw dna
llebpmaC nitniuQ ot rettel 2681 ,82 enuJ a ni nlocniL maharbA ~
$

If you wanted to display the last line as the first line and the first line as the last rather than reversing the characters on each line, you can use the tac command - "tac" is "cat" in reverse. E.g., for the same sample.txt file:

$ tac sample.txt
~ Abraham Lincoln in a June 28, 1862 letter to Quintin Campbell
and will regret it all your life.
you will lose the power of keeping any resolution,
On the contrary, if you falter, and give up,
Adhere to your purpose and you will soon feel as well as you ever did.
$

On a CentOS Linux system, the cat and tac commands are part of the coreutils package while the rev command is part of the util-linux package.

$ rpm -q --whatprovides /usr/bin/cat
coreutils-8.22-11.el7.x86_64
$ rpm -q --whatprovides /usr/bin/rev
util-linux-2.23.2-22.el7_1.x86_64
$ rpm -q --whatprovides /usr/bin/tac
coreutils-8.22-11.el7.x86_64
$

The util-linux package can be obtained using whatever package management utility you normally use for your distribution of Linux, e.g., yum for CentOS, or you can obtain the utility via FTP from the Linux Kernel Archive at ftp.kernel.org. You can login using "anonymous" as the userid and anything for the password, then type cd pub/linux/utils/util-linux to see the available versions.

[/os/unix/commands] permanent link

Wed, Aug 24, 2016 11:03 pm

Voice recognition software surpasses humans typing

I've had my current Android smartphone for several years, but have never tried its voice recognition features. I did try the feature on my prior phone, but after a few frustrating attempts to just have it call home when I said my wife's name, I deemed the feature useless to me; it was too aggravating to have the phone say something like "Did you say..." followed by something entirely unrelated. Though I might eventually get it to dial our home number, the process was more time consuming than for me to just type in the phone number. But after hearing an NPR report today while I was driving home on a recent study conducted jointly between researchers at Stanford University, the University of Washington and the Chinese search engine company Baidu that pitted humans typing on Apple iOS keyboards against Baidu's speech recognition software, I'll see how well the speech dictation software works on my current phone. The results of the study can be found on a Stanford University site at Speech Is 3x Faster than Typing for English and Mandarin Text Entry on Mobile Devices.

For the speech transcription method, the researchers used Baidu's Deep Speech 2 deep learning speech recognition system. The software took the spoken input and converted it to text. Recognition errors could then be corrected by the study participants by either speech or the smartphone's keyboard. That method was found to be three times faster than the participants relying solely on their typing skills on the keyboards for English and 2.8 times as fast for Mandarin Chinese. And, strikingly, the English error rate was 20.4% lower, and the Mandarin error rate 63.4% lower, than the keyboard method. I don't know Mandarin, but a 20.4% lower error rate for English is significant.

I took a typing class in high school - when I was in high school typewriters were still common - after the typing teacher stated that it would be useful for typing papers for those of us who hoped to go on to college. I bought a cheap typewriter in college, but didn't use it much, instead I had most of the papers I needed to be typewritten typed by a local high school teacher who, as a side business typed papers for the nearby university students at a nominal cost. She also proofread the papers, correcting spelling and grammar errors, which I felt was worth the cost of paying to have papers typed that would be an important part of my grade. But, though I didn't use the typing skills I learned in the high school typing class a lot for typing papers, I found those skills invaluable for the many later computer courses I took. So, I'm a fairly fast typist on a full size keyboard, but I'm very slow on the tiny keyboard on my phone and am akin to the sloth, Flash, in the movie Zootopia when compared to some of my nieces - one of my nephews bought a phone for his younger sister, but had to quickly change the text plan when she had 3,000 text messages one month. For her, typing her text messages might be faster than using the voice recognition feature on her phone, but, even though the voice recognition software on my phone is doubtless far less powerful than that of Baidu's Deep Speech 2, I'll try that feature of the phone, since I would also expect there has been improvement in the intervening years since I first tried the feature on a prior phone. As Baidu chief scientist Andrew Ng noted "Humanity was never designed to communicate by using our fingers to poke at a tiny little keyboard on a mobile phone. Speech has always been a much more natural way for humans to communicate with each other."

Ng also stated he looks forward to the day when his future grandchild comes home and asks, "Is it really true that when you were young, if you came home and you said something to your microwave oven — did it really just sit there and ignore you? That's just so rude of the microwave." As we move futher into the Internet of Things (IoT), I expect that people talking to their microwaves and other household appliances will become common.

A text version of the NPR article, which was broadcast on All Things Considered, is available at Voice Recognition Software Finally Beats Humans At Typing, Study Finds.

[/news] permanent link

Mon, Aug 22, 2016 11:45 pm

Substituting characters for a matched regular expression in vi

The vi editor is a screen-oriented text editor that supports regular expressions for pattern matching and character substitution. Vim which stands for "Vi IMproved" is a clone of vi and recognizes similar commands.

If you want to replace or insert characters at the beginning of a line, the line beginning is represented by the caret character, i.e., ^ (Shift-6 on a standard computer keyboard), and line endings are represented by the dollar sign character, i.e., $.

E.g., the following quote has three occurences of the word "us". If I wanted to replace only the "us" at the end of the line with "ourselves", I could hit the colon key while not in vi's insert mode, which would give me a colon prompt and then enter s /us$/ourselves/ which would replace the occurence of "us" at the end of the lne with "ourselves".

What lies behind us and what lies before us are tiny compared to what lies within us

~ Ralph Waldo Emerson

[ More Info ]

[/software/editors/vi] permanent link

Sat, Aug 20, 2016 9:57 pm

Changing the line spacing in Publisher 2013

To change the spacing between lines in Microsoft Publisher 2013, take the following steps:
  1. Click on Home at the top, left side of the Publisher window.
  2. Highlight the the text for which you wish to change the line spacing by clicking on the start of it and dragging the mouse pointer to the end of it.
  3. Click on the diagonally pointing arrow at the lower, right-hand corner of the Paragraph block.
  4. In the Paragraph options window, change the "between lines" value for line spacing.
  5. Click on OK.

[ More Info ]

[/software/office/2013/Publisher] permanent link

Fri, Aug 19, 2016 4:19 pm

Viewing Berkeley DB files

If you have .db files on a Linux system, they may be Berkeley DB (BDB) database files. Berkeley DB originated at the University of California, Berkeley as part of BSD, Berkeley's version of the Unix operating system. The initial release was in 1994. Berkely DB was futher developed by SleepyCat Software from 1996 to 2006. In February 2006, Oracle Corporation acquired SleepyCat and continued development of the software.

You can ascertain if a .db file is a BDB file using the file command. E.g., the Sendmail email software uses .db files stored in /etc/mail to control various aspects of the software's functionality. For instance, you can specify the domains for which Sendmail will accept email in the /etc/mail/local-host-names file or create "virtual users" using the /etc/mail/virtusertable file. But to alter Sendmail's behavior using these files, you need to generate .db files from the text files using the makemap command. E.g., makemap hash /etc/mail/virtusertable < /etc/mail/virtusertable. If you check the type of file for the .db file that will be created by the makemap utility with the file command, you will see the following information, if you check from the root account:

# file /etc/mail/virtusertable.db
/etc/mail/virtusertable.db: Berkeley DB (Hash, version 9, native byte-order)
#

[ More Info ]

[/software/database/berkeley_db] permanent link

Thu, Aug 18, 2016 10:46 pm

Bitdefender milter causing Sendmail restart failure

I needed to change the smart host setting for a Sendmail email server, so I edited /etc/mail/sendmail.mc and rebuilt /etc/mail/sendmail.cf with the m4 command. I then attempted to restart Sendmail, but it did not restart.

# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf
# service sendmail restart
Redirecting to /bin/systemctl restart  sendmail.service
Job for sendmail.service failed because the control process exited with error code. See "systemctl status sendmail.service" and "journalctl -xe" for details.

When I issued a systemctl status sendmail.service command for further information, I saw the following:

# systemctl status sendmail.service
● sendmail.service - Sendmail Mail Transport Agent
   Loaded: loaded (/usr/lib/systemd/system/sendmail.service; enabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Thu 2016-08-18 15:40:49 EDT; 11s ago
  Process: 25578 ExecStart=/usr/sbin/sendmail -bd $SENDMAIL_OPTS $SENDMAIL_OPTARG (code=exited, status=78)
  Process: 25573 ExecStartPre=/etc/mail/make aliases (code=exited, status=0/SUCCESS)
  Process: 25570 ExecStartPre=/etc/mail/make (code=exited, status=0/SUCCESS)
 Main PID: 3394 (code=exited, status=0/SUCCESS)

Aug 18 15:40:49 moonpoint.com systemd[1]: Starting Sendmail Mail Transport A....
Aug 18 15:40:49 moonpoint.com sendmail[25578]: 554 5.0.0 /etc/mail/sendmail....d
Aug 18 15:40:49 moonpoint.com sendmail[25578]: NOQUEUE: SYSERR(root): /etc/m...d
Aug 18 15:40:49 moonpoint.com sendmail[25578]: NOQUEUE: SYSERR(root): InputF...y
Aug 18 15:40:49 moonpoint.com sendmail[25578]: 451 4.0.0 InputFilter BitDefe...y
Aug 18 15:40:49 moonpoint.com systemd[1]: sendmail.service: control process ...8
Aug 18 15:40:49 moonpoint.com systemd[1]: Failed to start Sendmail Mail Tran....
Aug 18 15:40:49 moonpoint.com systemd[1]: Unit sendmail.service entered fail....
Aug 18 15:40:49 moonpoint.com systemd[1]: sendmail.service failed.
Hint: Some lines were ellipsized, use -l to show in full.

When I undid the changes I had made to sendmail.mc, the issue remained. When I used the journalctl command to check on the problem, I saw the following:

# journalctl -xe
-- 
-- Unit sendmail.service has failed.
-- 
-- The result is failed.
Aug 18 15:43:25 moonpoint.com systemd[1]: Dependency failed for Sendmail Mail Tr
-- Subject: Unit sm-client.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit sm-client.service has failed.
-- 
-- The result is dependency.
Aug 18 15:43:25 moonpoint.com systemd[1]: Job sm-client.service/start failed wit
Aug 18 15:43:25 moonpoint.com systemd[1]: Unit sendmail.service entered failed s
Aug 18 15:43:25 moonpoint.com systemd[1]: sendmail.service failed.
Aug 18 15:43:25 moonpoint.com polkitd[771]: Unregistered Authentication Agent fo
Aug 18 15:43:53 moonpoint.com sshd[25845]: Address 168.176.56.13 maps to wimax13
Aug 18 15:43:53 moonpoint.com sshd[25845]: Invalid user log from 168.176.56.13
Aug 18 15:43:53 moonpoint.com sshd[25845]: input_userauth_request: invalid user 
Aug 18 15:43:53 moonpoint.com sshd[25845]: pam_unix(sshd:auth): check pass; user
Aug 18 15:43:53 moonpoint.com sshd[25845]: pam_unix(sshd:auth): authentication f
Aug 18 15:43:55 moonpoint.com sshd[25845]: Failed password for invalid user log 
Aug 18 15:43:56 moonpoint.com sshd[25845]: Connection closed by 168.176.56.13 [p
lines 1490-1512/1512 (END)

[ More Info ]

[/network/email/sendmail] permanent link

Wed, Aug 17, 2016 11:55 pm

Starting the Windows 10 System Restore program from a command prompt

The Windows System Restore utility can be started from a command line interface (CLI) by typing the command rstrui at a command prompt.

Windows 10 System Restore

Click on Next to see available restore points.

Windows 10 System Restore Point

[/os/windows/win10] permanent link

Tue, Aug 16, 2016 10:09 pm

Changing the AutoSave time in Microsoft Publisher 2013

Microsoft Office applications, such as the desktop publishing application Microsoft Publisher, have a built-in autosave feature that will periodically save your work in progress at a set interval, so that you won't accidentally lose all the work you you've done while working on a document in the application in the event the application or the entire system crashes. The default setting for automatic saves in Publisher 2013 is ten minutes. To adjust that setting, take the following steps in Publisher:
  1. Click on File from the program's menu.
  2. Select Options.
  3. Click on Save.
  4. The default setting is to save any document changes every 10 minutes. Change the value to whatever you like and click on OK.

    Microsoft Publisher 
2013 autosave setting

[/software/office] permanent link

Mon, Aug 15, 2016 10:17 pm

Configuring Firewalld and Postfix on CentOS for SMTP connections

I needed to configure a NetScreen firewall to allow access to the Simple Mail Transfer Protocol (SMTP) port, port 25, on a CentOS 7 email server behind the firewall. After configuring the NetScreen firewall to allow SMTP connectivity, I found I still was not able to connect to the mail sever behind it from an external system. When I tested using Telnet, i.e., telnet 192.168.0.7 25, I saw a "no route to host" message.
$ telnet 192.168.1.7 25
Trying 192.168.1.7...
telnet: connect to address 192.168.1.7: No route to host
$

So I used the debug command on the NetScreen firewall to view traffic to the SMTP port, which showed me it was passing the traffic to the email server behind it. So I then checked the host-based software on the CentOS server. Since it was running CentOS 7, the default firewall management software on it is FirewallD. I first checked to see what services the firewall was allowing through and saw that SMTP wasn't included, so I added that to the allowed services and made it a permanent rather than temporary change. For permanent changes, the firewall software must be reloaded, so I then issued a reload command. Since I ran the commands from a normal user account, I was prompted to provide the root account password to add the service and reload the firewall software.

$ firewall-cmd --list-services
dhcpv6-client ssh
$ firewall-cmd --add-service=smtp --permanent
success
$ firewall-cmd --reload
success
$ firewall-cmd --list-services
dhcpv6-client smtp ssh
$

[ More Info ]

[/network/email/postfix] permanent link

Sun, Aug 14, 2016 10:41 pm

COUNTIFS with an "or" condition

I have an Excel spreadsheet where I track firewall rule requests. Column B in the spreadsheet tracks the status of requests that have been submitted. A request can have a status of "modified", "pending", "approved", "denied", "completed", or "implement removal". Column G contains the dates when a request was either approved or denied. I could calculate how many requests I approved or denied since a particular date by putting that date in cell F947. I use a COUNTIFS function, which allows you to count the number of instances where an entry in a spredsheet meets multiple criteria. E.g., the value in column B for a row is greater than 10 and, also, the value in column C is "Jane". I use the formula =COUNTIFS(G2:G932,">="&F947, B2:B932,"Denied") to calculate all the entries that have been denied since a particular date. E.g., if cell F947 contains the date 8/10/2016, I can count all the rows starting with G2, since the first row is a header row, up through the last entry where the date in column 2 is greater than or equal to August 10, 2016 and the status in column B is "Denied". I can also calculate the number of requests I've dealt with since that date with =COUNTIF(G2:G932,">="&F947), i.e., I have Excel count any entries where the date is greater than or equal to the date specified in cell F947. I can also count the number of requests with a particular status that indicates the request was approved, but then might have been implemented, which would send it to the "Completed" state or which had been approved, but, because the approval was for the removal of rules from firewalls, went to the "Implement Removal" state with the following:

=COUNTIFS(G2:G931,">="&F947,B2:B931,"Approved")

=COUNTIFS(G2:G931,">="&F947,B2:B931,"Completed")

COUNTIFS(G2:G931,">="&F947,B2:B931,"Implement Removal")

All of the above indicate that the request was approved, though the status for the request might not be listed as "Approved" in the system used to manage the requests, but could, instead be shown as "Completed" or "Implement Removal".

But I also wanted to have a cell where Excel would provide a total for the number of requests that were in any of the above states where the date for the request in the G column was on or after the specified date. To do so, I had to "sum" multiple "countifs" statements, since I couldn't find a way to easily put an "and" or "or" logical condition within a countifs statement. I was able to get the total with the below forumula:

=SUM(COUNTIFS(G2:G931,">="&F947,B2:B931,"Approved"), COUNTIFS(G2:G931,">="&F947,B2:B931,"Completed"), COUNTIFS(G2:G931,">="&F947,B2:B931,"Implement Removal"))

[/software/office] permanent link

Sat, Aug 13, 2016 9:38 pm

Determining which repository a package comes from

If you want to determine which software repository a package can be found in from a CentOS Linux system, you can use the repoquery command or yum info commands. A package doesn't have to be installed on the system for you to determine which repository it can be found in.

[ More Info ]

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

Fri, Aug 12, 2016 10:41 pm

Installing Amarok on a CentOS system

If you would like to have a free and open source, cross-platform, music player for use on a Linux system, Amarok , which was created by Mark Kretschmann, provides the capability to play various audio media files, such as MP3, FLAC, Ogg, AAC, etc. It also allows you to stream online music from services such as Jamendo, Shoutcast, etc.

To install Amarok on a CentOS Linux system using the yum package management utility, you will first need to configure the system to check the EPEL repository for packages. Once you have done that, you can issue the command yum install amarok from the root account to install the software.

[ More Info ]

[/software/audio_video/Amarok] permanent link

Wed, Aug 10, 2016 10:38 pm

DHCP Reserved Address from NetScreen Firewall

A Juniper Networks NetScreen firewall/router can be configured to function as a DHCP server; for the method to do so from a command line interface (CLI), which you can obtain by a Secure Shell (SSH) connection to the device, see Using a Juniper Networks NetScreen Firewall as a DHCP Server. The system can assign addresses dynamically from a pool of addresses you select or you can have it assign a reserved, i.e., fixed, address based on the media access control (MAC) address of the system requesting a DHCP-assigned IP address.

You can determine what addresses have already been assigned to systems via DHCP using a command in the form get interface <interface> dhcp server ip allocate where interface is a particular interface, e.g., trust, untrust, etc.

ns5xp-> get interface trust dhcp server ip allocate
       IP         	State	     MAC     	Lease Time
 192.168.0.34   	COMMIT	*000d560e185e	3236 minutes
 192.168.0.35   	COMMIT	*4c72b99cb82a	3925 minutes
ns5xp->

If I wished to assign the IP address 192.168.0.7 to the system above with MAC address 4c72b99cb82a, I could use the command below:

set interface trust dhcp server ip 192.168.0.7 mac 4c72b99cb82a

[ More Info ]

[/security/firewalls/netscreen] permanent link

Tue, Aug 09, 2016 10:26 pm

SSH break-in attempt from 221.229.172.35

When I checked the fail2ban log on one of my servers today, I found that fail2ban had banned IP address 221.229.172.35 for failed attempts to log into the system via Secure Shell (SSH).

# tail -n 10 /var/log/fail2ban.log
2016-08-09 10:12:56,296 fail2ban.filter         [1590]: INFO    [sshd] Found 221.229.172.35
2016-08-09 10:12:57,914 fail2ban.filter         [1590]: INFO    [sshd] Found 221.229.172.35
2016-08-09 10:12:58,663 fail2ban.filter         [1590]: INFO    [sshd] Found 221.229.172.35
2016-08-09 10:12:59,143 fail2ban.filter         [1590]: INFO    [sshd] Found 221.229.172.35
2016-08-09 10:12:59,870 fail2ban.actions        [1590]: NOTICE  [sshd] Ban 221.229.172.35
2016-08-09 10:13:00,591 fail2ban.filter         [1590]: INFO    [sshd] Found 221.229.172.35
2016-08-09 10:13:01,298 fail2ban.filter         [1590]: INFO    [sshd] Found 221.229.172.35
2016-08-09 10:13:01,522 fail2ban.filter         [1590]: INFO    [sshd] Found 221.229.172.35
2016-08-09 10:13:03,538 fail2ban.filter         [1590]: INFO    [sshd] Found 221.229.172.35
2016-08-09 10:13:04,075 fail2ban.filter         [1590]: INFO    [sshd] Found 221.229.172.35
#

When I checked the country where that IP address is assigned using the geoiplookup tool, I found it is assigned to an entity in China. The tool is in GeoIP, a geolocation package, which can be installed on Red Hat derived distributions of Linux, such as CentOS with yum install geoip. The free version of the software which I use is provided by MaxMind

$ geoiplookup 221.229.172.35
GeoIP Country Edition: CN, China
$

[ More Info ]

[/security/attacks/ssh] permanent link

Mon, Aug 08, 2016 10:09 pm

Using dhclient to locate DHCP Servers on a LAN

On a Linux system, you can use the dhclient command to identify any Dynamic Host Configuration Protocol (DHCP) servers that are available on the local area network (LAN). First, you need to determine a relevant network interface on the system over which an IP address might be acquired via DHCP. You can do so using the ip command. If the -f inet option is given to the command, it will show only IPv4 addresses.

# ip -f inet address
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN 
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: enp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    inet 192.168.0.35/24 brd 192.168.0.255 scope global dynamic enp4s0
       valid_lft 156092sec preferred_lft 156092sec
3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN 
    inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
       valid_lft forever preferred_lft forever

Alteratively, you can use the ifconfig command with the -a option to show all network interfaces and any assigned IP addresses for them. I.e., ifconfig -a.

In the example above from a CentOS 7 system, I can see that an IP address is assigned to the enp4s0 network interface and that is the interface I will use for the DHCP query to locate any DHCP servers on the network, which may be legitimate or rogue DNS servers.

To have the dhclient command search for DHCP servers, I'll use the -d and -nw options.

[ More Info ]

[/network/dhcp] permanent link

Sun, Aug 07, 2016 8:35 pm

Postfix commands

You can usually determine what mail transfer agent software is running on an email server by using Telnet to connect to the mail server on the Simple Mail Transfer Protocol (SMTP) port, port 25. E.g., in the example below Postfix is handling email on the system.

# telnet 127.0.0.1 25
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
220 jinn.localdomain ESMTP Postfix
quit
221 2.0.0 Bye
Connection closed by foreign host.
#

You can enter SMTP commands that other email servers would issue to send an email to a local user on the system as shown below:

# telnet 127.0.0.1 25
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
220 jinn.localdomain ESMTP Postfix
ehlo Me
250-jinn.localdomain
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
mail from: tester@example.com
250 2.1.0 Ok
rcpt to: joe
250 2.1.5 Ok
data
354 End data with <CR><LF>.<CR><LF>
From: tester22@example.com
To: joe@example.com
Subject: Just a test
This is only a test.
.
250 2.0.0 Ok: queued as B27928276DA1
quit
221 2.0.0 Bye
Connection closed by foreign host.
$

[ More Info ]

[/network/email] permanent link

Sat, Aug 06, 2016 10:37 pm

Dovecot not accepting passwords

A user reported that email was not working. So I logged into an account on the CentOS 7 email server and connected to port 25, the Simple Mail Transport Protocol (SMTP) port, via Telnet to ensure that the server was responding to SMTP connections.
$ telnet 127.0.0.1 25
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
220 moonpoint.com ESMTP Sendmail 8.14.7/8.14.7; Sat, 6 Aug 2016 09:26:06 -0400
quit
221 2.0.0 moonpoint.com closing connection
Connection closed by foreign host.
$

Since the Sendmail SMTP service seemed to be functioning properly, I next checked the Dovecot POP3/POP3S software on the system. I entered the commands an email client would submit to authenticate with the server on the POP3 port, port 110, i.e., pass followed by the user's login id then pass and the password for the user's account. I received an immediate response to the user command, but when I entered the pass command followed by the password and hit Enter I didn't see any response even after waiting much longer than I would expect to have to wait for a response. So I hit Ctrl-], i.e., the Ctrl and ] keys to return to the Telnet prompt and then exited from the telnet program.

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[/network/email/dovecot] permanent link

Fri, Aug 05, 2016 10:45 pm

Konqueror Saved Sessions Location

The Konqueror web browser, which is available for Linux and Microsoft Windows systems, provides a mechanism to save and restore sessions. If Konqueror becomes unresponsive and you have to kill it, you should be given a choice to restore the previous session when you reopen the browser.

You can manually save a session, by clicking on File on the menu bar, then selecting Sessions, then Save As.... You will then be prompted to provide a name for the session. You can reopen a saved session by selecting File then Sessions from the menu bar and then selecting from one of the saved sessions you will see listed. If you have previously saved one or more sessions, you will see them listed under the Save As... and Manage... options.

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[/network/web/browser/konqueror] permanent link

Thu, Aug 04, 2016 10:53 pm

Using the zipinfo command

If you wish to view a list of the files contained in a zip file, i.e., one with a .zip extension, on Linux and Mac OS X systems you can use the zipinfo command. If you enter the command zipinfo followed by the name of the zip file, you will see a Unix-style file listing for each compressed file contained within the zip file.

$ ls -l vnc-osx.zip
-rw-r--r--. 1 joe joe 57641 Jun 28  2013 vnc-osx.zip
$ zipinfo vnc-osx.zip
Archive:  vnc-osx.zip
Zip file size: 57641 bytes, number of entries: 4
drwxr-xr-x  3.0 unx        0 bx stor 13-Jun-28 12:43 vnc/
-rw-r--r--  3.0 unx    21375 bx defN 13-Jun-27 20:31 vnc/Connect_to_Server.png
-rw-r--r--  3.0 unx    36303 bx defN 13-Jun-27 20:33 vnc/Enter_Name_Password.png
-rw-r--r--  3.0 unx     2834 tx defN 13-Jun-28 12:43 vnc/vnc-remote-access.html
4 files, 60512 bytes uncompressed, 56943 bytes compressed:  5.9%
$

In the example above you can see that there are three files stored in the zip file; the output indicates 4 files because the directory, vnc, is counted as a file on a Unix system. The total bytes for the four files before they were compressed into a zip file is 60,512 bytes. They were compressed down to 56,943 bytes, which is a 5.9% compression ratio, since (60512 - 56943) / 60512.0 * 100 = 5.9.

If you just wish to see the file and directory names contained in the zip file, you can use the -1 argument (that's the number one).

$ zipinfo -1 vnc-osx.zip
vnc/
vnc/Connect_to_Server.png
vnc/Enter_Name_Password.png
vnc/vnc-remote-access.html
$

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[/os/unix/commands] permanent link

Wed, Aug 03, 2016 10:22 pm

GIMP Color Picker

I wanted to determine the hexadecimal or RGB values for the text in a Terminal window on a CentOS 7 Linux system. I didn't have gpick or another color picker utility available, but I did have the GNU Image Manipulation Program (GIMP) already installed on the system (you can install it on a CentOS system with yum install gimp), so I was able to take a screenshot of the window with GIMP and then use GIMP's color picker tool to determine the color of the text. To access the color picker tool, select Tools and then Color Picker from the GIMP menu.

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[/software/graphics/gimp] permanent link

Mon, Aug 01, 2016 11:08 pm

Determining the version of Microsoft Windows from the command line

You can determine the version of Microsoft Windows on a system from a command line interface (CLI), e.g., a command prompt, using the systeminfo command. Since that command will provide a lot of other information on the system, you can filter the output to see only the operating system (OS) version by piping its output into the findstr command using the "|" pipe character. The command below will show only the operating system version:
C:\>systeminfo | findstr /R "^OS.Version"
OS Version:                10.0.10586 N/A Build 10586

C:\>

The /R option indicates that the findstr command should perform its search based on a regular expression. The "^" character is a character that when included in a regular expression means that what follows should be at the beginning of the line. Without it, you could see something like the following, instead, since "BIOS Version also matches:

C:\>systeminfo | findstr /R "OS.Version"
systeminfo | findstr /R "OS.Version"
OS Version:                10.0.10586 N/A Build 10586
BIOS Version:              Dell Inc. A04, 11/21/2011

C:\>

The period between "OS" and "Version" indicates in a regular expression that any one character in that space will match; in this case there is a space character between the two words, which will match the period in a regular expression. If you want to have a period treated as a period rather than serving its function as a regular expression character, you can "escape" its meaning by using the backslash, i.e. "\", escape character.

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[/network/email/sendmail] permanent link

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