Apple UNIX

The underwater operating system of Apple SnowLeopard is based on Unix. So use the power of Unix in Apple Mac.

Useful Unix Utilities

Program	Description	Usage Example
bc	Basic Calculator, type 2+2 and press return.
kill	Max OS X offers no shortage of ways to cut the cord on programs that seems to be locked up or running amok. Use the Activity Monitor or use kill. First get the ID number running top.
open	Launch programs
ps	Process Status (ps) is another way to get a quick look at all running programs. For the best results use the -e and the -f flags.	ps -ef
shutdown	Shutdown with the -h flags has its advantages, because it gives the user more control.	shutdown -h
tar, gzip, zip	Compressed Archive files
top	Running top (table of processes) lists every program currently running.	top -u
xattr	Manage the extended attributes of Mac files, invisible metadata describing all kind of characteristics of every file.
alias	Shortcuts for commands	alias la='ls -Al'
nano, emacs, vim	editors
grep	Grep is a filter and is used in combination with other programs.
find	Terrible powerful program with a lot of features.	find . -name "fn" -type f -print 2>/dev/null
mdfind	MedaData find	mdfind 'kMDItenFlashOnOff == "1"'
launchd	Launching System Programs
ftp	File Transfer Program

Example Process Finding

If you are running a terminal program, you may wanna find if it is still running using one of the above tools.
Assume you are running the following program which runs in an infinite loop (forever) in a Terminal window.

$ php FormulaExec.php

To see the program PID you can use:

$ ps -e 
  PID TTY           TIME CMD
    1 ??         2:44.97 /sbin/launchd
   46 ??         0:48.23 /usr/sbin/syslogd
  ...
  528 ttys000    0:01.81 login -pfl HaFrMpro /bin/bash -c exec -la bash /bin/bash
  542 ttys000    0:00.08 -bash
 3002 ttys000    0:00.01 tail -f -n 64 /Applications/MAMP/logs/php_error.log
  536 ttys001    0:01.76 login -pfl HaFrMpro /bin/bash -c exec -la bash /bin/bash
  644 ttys001    0:00.18 -bash
10842 ttys001    0:00.11 php FormulaExec.php
  537 ttys002    0:01.77 login -pfl HaFrMpro /bin/bash -c exec -la bash /bin/bash
  668 ttys002    0:00.76 -bash
10969 ttys002    0:00.00 ps -e
   ...
$

If you use:

$ ps -e | grep -i 'formulaexec'
10842 ttys001    0:00.12 php FormulaExec.php
11001 ttys002    0:00.01 grep -i formulaexec
$ 

Alternative you can use the top command which opens a monitor on top of the screen (ends by Ctrl-C):

$ top
top - 15:43:44 up 41 days, 20:28,  0 users,  load average: 4.22, 4.07, 3.55
Tasks:   2 total,   1 running,   1 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.5 us,  6.8 sy, 37.5 ni, 54.8 id,  0.1 wa,  0.0 hi,  0.4 si,  0.0 st
KiB Mem:  32142684 total, 30160744 used,  1981940 free,     1712 buffers
KiB Swap:        0 total,        0 used,        0 free, 24802844 cached

   PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND                                                           
     1 harmfrie  20   0 17956 3220 2664 S   0.0  0.0   0:00.19 bash                                                              
     7 harmfrie  20   0 21684 2328 1900 R   0.0  0.0   0:00.02 top                                                               

Prevent hangup

Closing the terminal kills the process.
Can I run a command in such a way that I can close the terminal without killing the process? The answer is the programs nohup and disown.

$ nohup redshift &

or

$ redshift &
$ disown

or

$ sleep 1000
^Z
[1]+  Stopped                 sleep 1000
$ bg
$ disown
$ exit

All of the above may not work properly, try instead:

# Suppose for some reason Ctrl+Z is also not working, go to another terminal, find the process id (using ps) and run:
# The command kill -20 (SIGTSTP) will suspend the process 
$ kill -20 PID 
# The command kill -18 (SIGCONT) will resume the process, in background.
$ kill -18 PID
# So now, closing both your terminals won't stop your process.
# Just remember to do the disown %1 in the first terminal before closing it. 

See

• Computerhope.com ups

Server Broken Pipes

For keeping the connection alive, you can check in /etc/ssh_config the line where it says ServerAliveInterval, that tells you how often (in seconds) your computer is gonna send a null packet to keep the connection alive.
If you have a 0 in there that indicates that your computer is not trying to keep the connection alive (it is disabled), otherwise it tells you how often (in seconds) it is sending the aforementioned packet.
Try putting 120 or 240, if it is still killing your connection, you can go lower, maybe to 5, if with that number it doesn't happen, maybe it is your router who is dumping the connection to free memory.

Example

ServerAliveInterval 10

See

• Apple StackExchange, Prevent ssh session from hanging.

Screen

Screen is a full-screen software program that can be used to multiplexes a physical console between several processes (typically interactive shells). It offers a user to open several separate terminal instances inside a one single terminal window manager.

Entering Screen

# Enter screen
$ screen

# Do something such as installing something
$ git clone xxxx

# Detach your screen using Ctrl-A-d
[detached]
$ 

# Re-Attach Screen using
$ screen -r

The screen application is very useful, if you are dealing with multiple programs from a command line interface and for separating programs from the terminal shell. It also allows you to share your sessions with others users and detach/attach terminal sessions.

Leaving Screen

There are 2 (two) ways to leaving the screen.

• Ctrl-A and D to detach the screen.
• Ctrl-A and K to kill the screen.

That’s some of screen usage on daily basis. There are still a lot of features inside the screen command. You may see screen man page for more detail.

• TecMint Screen. Command examples to manage Linux terminals TecMint Screen.

cron replacement

Cronjobs and other deamons are not allowed on most Hosting Service Providers. An alternative maybe EasyCron and setcronjob

• easycron, has a free plan for simple cronjobs.
• setcronjob, not free and has the same functionality as easycron.