Pardon me while I brag a little bit.

Well, no, not really brag. Honestly, I'm just astonished to find my Unix and Linux Troubleshooting E-Book listed among the "best sellers" in not one, but two Amazon categories. Ok, in fairness it barely makes the cutoff in Books>Computers & Technology>Operating Systems>Unix, but it's on page two of Kindle Store>Kindle eBooks>Computers & Technology>Operating Systems>Unix and that surprises me.

OK, it's not exactly like it was Books>Computers & Technology>Operating Systems>Linux, but even there it is not all that far from the magic 100 mark. This book is much more popular than I thought.

I guess I shouldn't be too surprised as Amazon has been sending me money all these years and it's not like any of those are very crowded categories, but still: it's a best seller and I'm going to stick that little feather in my cap and call attention to it.

If you don't mind spending a whopping $2.99 for what one reviewer called "Whimsical, entertaining, yet informative", you could even help me drive it higher!

Linux and Unix Troubleshooting Kindle Edition

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Anonymous asks:

Why doesn't rcp work for root? I get Permission Denied even though it works with other users?

Before I answer that, I'd like to first suggest that you forget about rcp and use scp. Unless the system you are using is too old to support ssh and scp, you really should not use rcp.

So my answers assume you cannot. The first thing to understand is that root has special rules. One is that you must use a .rhosts file in root's HOME directory. It must be owned by root and must be 0600 perms.

Be sure that root's HOME is where you think it is!

You also need to realize that any system names you put in .rhosts have to match what the system sees. Check by pinging the ip of the other site.

Another requirement is that root be allowed to login remotely. That may require an entry in /etc/securetty on some systems and you may also need to allow it in Selinux if that is enabled.

Obviously any firewalls in the way need to allow this and the rsh service has to be started or enabled in whatever functions as the super daemon on your system. As I'm assuming you are using something too old for ssh, that's probably /etc/inetd.conf or an /etc/xinetd.d file.

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Anonymous asks:

How can I prevent logins? I need a way to disable logins from the root user account without being at the server console itself.

Many modern Unix/Linux systems respect the /etc/nologin file. Simply login as root and do "touch /etc/nologin". This restricts logins to root only. When you want to allow users again, "rm /etc/nologin".

Many systems also allow you to add text to /etc/nologin. When users attempt to login, they see that text.

$ ssh tonyl@aplawrence.com


Logins currently not allowed.

Check back in an hour or so, thanks.

Older systems like SCO Unix don't have that. For these systems, you need to add code to /etc/profile. For example, you could add this:

IAM=`who am i | cut -d" " -f1`
[ -f /etc/nologin ] && [ $IAM ] && [ $IAM != "root" ] && exit 0

The danger here is that you mistype that code - you could easily lock yourself out forever. I recommend not exiting the editor until you have tested thoroughly.

But what about users already logged in? That code doesn't affect them at all.

That can be trickier. You can write scripts to loop through logged in users and kill them off. A more drastic but easy solution is to "touch /etc/login" and then do a shutdown and reboot.

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Anonymous asks:

Where can I get a hexadecimal or binary calculator that will help me manage hex and binary numbers?

Do you mean like this?

That's just the standard Calculator App on Mac OS X after hitting Command+3. The standard Windows 7/8 calculator has a very similar switching capability.

On Linux, most people recommand qalculate.

There is a whole pile of choices on Android - just Google!

There are also many listed in the IOS App store, but Pcalc seems to be the clear leader. You can add a $2.99 Programmer Pack to the free Lite Version or get the full version (which includes that and more) for $9.99.

Qalculate is a Powerful Calculator For Linux

The Calculator in Windows 7 & Windows 8 - A Tool for the Geek in You!

Switch Between Three Calculators on OS X with a Keyboard Shortcut

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Xinuos has introduced Open Server X, a BSD distro that they describe as a "migration path" for SCO UnixWare 7, SCO OpenServer 5 and SCO OpenServer 6 customers. If this had been offered ten years ago, it might have been of interest, but I really have a hard time imagining this will matter at all now. Still, I downloaded the image and fired it up in a VM.

And that was as far as I went. I simply cannot imagine myself suggesting that anyone now stuck on an older SCO OS take a look at this. Why would they? What possible advantage could there be? I don't see any - if I'm wrong, please do tell me in the comments.

Update Decenber 2015: John Boland added this:

As an old System V programmer, I've been interested in the SCO products as descendants of SysV and have at various times installed and done no more than play around with Openserver 5 and Unixware 7. Starting up X I was momentarily shocked to see the familiar FreeBSD opening lines and quickly realised that's what it is. But what I now think is that it's a relatively painless way of installing a FreeBSD desktop, complete with Xfce. Almost everything you might want can be installed easily from the DVD and, apart from some later messing around to get wifi going, it all went quite smoothly. Once installed, I've seen it essentially as FreeBSD but with that somewhat Solaris 10-like Administration program. Anyway, we'll see.

Xinuos Announces OpenServer X Operating System to Deliver Enterprise-Class Solutions to Companies of Any Size

OpenServer X

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I've been seeing frightening headlines about a new threat to Linux based routers. "Moose - the router worm with an appetite for social networks", "Dissecting the Linux/Moose malware", "Moose worm targeting Linux-based routers and systems" and more. Bar the door and get out the rifles, boys: we are under attack!

There's even an imposing list of "affected vendors": 3Com, Alcatel-Lucent, Allied Telesis, Avaya, Belkin, Brocade, Buffalo, Celerity, Cisco, D-link, Enterasys, Hewlett-Packard, Huawei, Linksys, Mikrotik, Netgear, Meridian, Nortel, SpeedStream, Thomson, TP-Link, Zhone, ZyXEL and more. Forget the rifles, we need cannons!

Really? According to an Arstechnica article that came complete with a scary graphic, the Linux/Moose malware "exploits routers open to connections from the Internet via Telnet by performing brute-force login attempts using default or common administrative credentials".

Say what? Telnet? Default credentials?

Honestly, how can you look at me with a straight face and call this a Linux security issue? ANY ROUTER WITH DEFAULT CREDENTIALS IS A SECURITY THREAT! This isn't a Linux security issue; it's an idiot's security issue!

On my systems, I'm meeting this threat head-on by doing absolutely nothing. I never had telnet open to start with and default credentials were changed before any of my routers first connected to the internet. Linux security threat? Nonsense.

The Moose is loose: Linux-based worm turns routers into social network bots

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This is a continuation of Unix and Linux startup scripts, Part 3

Systemd is gaining favor in Linux distributions. This is a big change from inittab and everything else we've had in the past. To find out more about it, I downloaded the latest Ubuntu desktop and began exploring. The first thing I noticed is that there is still an init.d directory and it does have shell scripts in it. However, /sbin/init is now a symlink to /etc/systemd and those scripts do not execute when systemd is in charge.

Note that the Advanced Options section of the Grub menu will let you boot with Upstart. You'll need to edit your /etc/default/grub file to put a "#" ahead of GRUB_HIDDEN_TIMEOUT=0 and do a "sudo update-grub" to have that option.

As systemd certainly can execute shell scripts, I wondered if it might be piggybacking these. It isn't: I modified /etc/init.d/rc.local to add "date >> /home/tony/booted". That runs if I boot with Upstart, but not with systemd. So how would you do something simple like that?

Systemd has its own directory, /etc/systemd. There are various files and sub-directories. In the sub-directories are the "service" files (called units in much documentation) that control startup. I noticed a "user" directory and figured that might be a good place to add my own little test, but apparently it isn't necessarily. See systemd/User. So I created it in my home directory.

[Unit]
Description=Tony's date stamper

[Service]
ExecStart=/home/tony/tonyapp

[Install]
WantedBy=multi-user.target

The Description will appear in logs. The ExecStart is what I want to happen and WantedBy tells it when. There are other possible targets: poweroff.target (when system is going down, like run-level 0), rescue.target (single user, init 1), multi-user.target (init 2-4), graphical.target (init 5) and reboot.target (init 6). ExecStart could be a binary, a shell script - but note that you must include the full path and that the environment is empty - no variables are set. If you must set variables, add an EnvironmentFile= line pointing at something that sets them or use Environment="XYZ=7" 'YY=hello there' for simple cases. After adding this file, I enabled it with "sudo systemctl enable /home/tony/tonyapp.service". I could force it to run right now with "systemctl start tonyapp".

Note that this won't try to restart because there is nothing in the service file to say that it should. There are many, many other control words you can use. You can specify that other services must start before this and that others must be after. Service files can be quite complex; you can learn more by looking in the /etc/systemd/system directory. You can ask about the status of any service with (for example):

$ systemctl status tonyapp
● tonyapp.service - Tony's date stamper
   Loaded: loaded (/home/tony/tonyapp.service; enabled; vendor preset: enabled)
   Active: inactive (dead) since Tue 2015-05-12 06:56:36 PDT; 10min ago
  Process: 1417 ExecStart=/home/tony/tonyapp (code=exited, status=0/SUCCESS)
 Main PID: 1417 (code=exited, status=0/SUCCESS)

May 12 06:56:36 ubuntu systemd[1]: Started Tony's date stamper.
May 12 06:56:36 ubuntu systemd[1]: Starting Tony's date stamper...

That tells us everything we'd need to know! Other services may give even more information:

$ systemctl status sshd
● ssh.service - OpenBSD Secure Shell server
   Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2015-05-12 06:50:56 PDT; 17min ago
  Process: 955 ExecReload=/bin/kill -HUP $MAINPID (code=exited, status=0/SUCCESS)
 Main PID: 708 (sshd)
   CGroup: /system.slice/ssh.service
           └─708 /usr/sbin/sshd -D

May 12 06:50:56 ubuntu systemd[1]: Started OpenBSD Secure Shell server.
May 12 06:50:56 ubuntu systemd[1]: Starting OpenBSD Secure Shell server...
May 12 06:50:57 ubuntu sshd[708]: Server listening on 0.0.0.0 port 22.
May 12 06:50:57 ubuntu sshd[708]: Server listening on :: port 22.
May 12 06:50:57 ubuntu sshd[708]: Received SIGHUP; restarting.
May 12 06:50:57 ubuntu systemd[1]: Reloaded OpenBSD Secure Shell server.
May 12 06:50:57 ubuntu sshd[708]: Server listening on 0.0.0.0 port 22.
May 12 06:50:57 ubuntu sshd[708]: Server listening on :: port 22.
May 12 06:52:56 ubuntu sshd[1283]: Accepted password for tony from 10.211.55.2 port 58485 ssh2
May 12 06:52:56 ubuntu sshd[1283]: pam_unix(sshd:session): session opened for user tony by (uid=0)

You can get a simple status list with "systemctl list-unit-files --type=service"

Note the STATE column. Possible states are:

• enabled
• disabled
• static - enabled if something else wants it, disabled otherwise. Its unit file does not contain an "install" section.
• masked - disabled and cannot be started. "systemctl mask tonyapp.service" would prevent it starting, "systemctl unmask tonyapp.service" restores normalcy
• linked - Came from a symlink to the unit file by "systemctl link SOMEUNITFILE". The unit file is now available for start and other commands although it is not installed directly in the unit search path.
• failed
• enabled-runtime - enabled for only this boot of the system
• linked-runtime - linked for only this boot of the system
• masked-runtime - masked for only this boot of the system
• indirect - Unit file itself is not enabled, but it has a non-empty Also= setting in the "[Install]" section. That keyword allows units to be treated as a set.

That "masked" seems to be done by symlinking to /dev/null.

So could you use SysV init scripts? Yes, but with some caveats: Compatibility with SysV. Unlike SysV, scripts cannot hang. By default, they are stopped in 5 minutes (can be changed with TimeoutStopSec= or in sysytemd conf files). Let me mention again that the environment is clean - nothing set at all. Also, systemd won't try to stop a service that is not already running.

By the way, your unit file specifies how things are stopped with KillMode= and a few other directives.

Switching to targets is easy: "systemctl isolate rescue.target". In addition to that, systemctl takes arguments like "reboot", "default", "suspend", "hibernate" and more.

Systemd can also start things when other things happens. It functions as the (x)inetd super daemon did for network connections. It can start a service when a file is created and much more. I have barely scratched the surface here.

I like systemd. I learned BSD init and SysV inittab thirty-five years ago, but I see no need to be stubborn about it: this is better. I didn't like Upstart or any of the other replacement wanna-be's, but systemd makes sense.

It's optional for now, but Linux Mint expects to switch to systemd next year

Grab your pitchforks: Ubuntu to switch to systemd on Monday

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