Broke up long lines

cron_101.rst

@@ -2,36 +2,59 @@
 Crontab
 #######
 
-Laziness is considered a virtue in system administration, meaning you should figure out ways to avoid having to perform the same task regularly by hand. **Cron** to the rescue!
-
-    **cron** is the time-based job scheduler in Unix-like computer operating systems. **cron** enables users to schedule jobs (commands or shell scripts) to run periodically at certain times or dates. It is commonly used to automate system maintenance or administration, though its general-purpose nature means that it can be used for other purposes, such as connecting to the Internet and downloading email. [#]_
-
-**cron** allows you to run routine jobs on a user's system automatically at a specific future time or at regular intervals rather than running such jobs manually. Even knowing just the basics of crontab is a huge win, as this tool increases productivity, saves time and is not prone to human error, i.e. forgetting to run a job.
+Laziness is considered a virtue in system administration, meaning you should
+figure out ways to avoid having to perform the same task regularly by hand.
+**Cron** to the rescue!
+
+    **cron** is the time-based job scheduler in Unix-like computer operating
+    systems. **cron** enables users to schedule jobs (commands or shell scripts)
+    to run periodically at certain times or dates. It is commonly used to
+    automate system maintenance or administration, though its general-purpose
+    nature means that it can be used for other purposes, such as connecting
+    to the Internet and downloading email. [#]_
+
+**cron** allows you to run routine jobs on a user's system automatically at a
+specific future time or at regular intervals rather than running such jobs
+manually. Even knowing just the basics of crontab is a huge win, as this tool
+increases productivity, saves time and is not prone to human error, i.e.
+forgetting to run a job.
 
 What is a "crontab"?
 ====================
 
-"crontabs" (or *cron tables*) are the way that a user schedules a job to run under **cron**. They're composed of the following parts:
+"crontabs" (or *cron tables*) are the way that a user schedules a job to run
+under **cron**. They're composed of the following parts:
 
-- *cron expression*: A string that describes the time or times when the command should be run
-- *user* (optional): If the crontab is specified in a centralized location instead of the user's personal crontab file, this field contains the username that the command should be run as. This allows **cron** to run a command as you, even if you're not logged in at the time. This field isn't used in a user's personal crontab file.
-- *command*: The rest of the line is interpreted as the command that **cron** should run at the specified time.
+- *cron expression*: A string that describes the time or times when the command
+  should be run
+- *user* (optional): If the crontab is specified in a centralized location
+  instead of the user's personal crontab file, this field contains the username
+  that the command should be run as. This allows **cron** to run a command as
+  you, even if you're not logged in at the time. This field isn't used in a
+  user's personal crontab file.
+- *command*: The rest of the line is interpreted as the command that **cron**
+  should run at the specified time.
 
-"crontab" may also refer to a file containing any number of these "crontabs", one per line.
+"crontab" may also refer to a file containing any number of these "crontabs",
+one per line.
 
 The ``crontab`` command
 =======================
 
 How do I list jobs scheduled to run with **cron**?
 --------------------------------------------------
 
-The easiest way to see jobs running regularly on the current user's system (aka "cron jobs") is to type:
+The easiest way to see jobs running regularly on the current user's system
+(aka "cron jobs") is to type:
 
 .. code-block:: bash
 
   crontab -l
 
-in the shell. This will show all the cron jobs that currently run on the current user's system. For example, if you are logged in as ``jdoe``, then the current user is ``jdoe``, and if there are no cron jobs running the output will be something like:
+in the shell. This will show all the cron jobs that currently run on the current
+user's system. For example, if you are logged in as ``jdoe``, then the current user
+is ``jdoe``, and if there are no cron jobs running the output will be something
+like:
 
 .. code-block:: console
 
@@ -53,7 +76,8 @@ The way to schedule a new job is to type:
 
   crontab -e
 
-in the shell. This will open an editor with your personal "crontab" file (or an empty file if you don't have any cron jobs already scheduled).
+in the shell. This will open an editor with your personal "crontab" file (or
+an empty file if you don't have any cron jobs already scheduled).
 
 Then add a line to the file that looks like this:
 
@@ -63,7 +87,10 @@ Then add a line to the file that looks like this:
 
 and save and close the file.
 
-The cron job you just created will run the command ``date`` at the top of every hour (e.g. at 10:00, 11:00, 12:00, etc.). Depending on how your system is configured, it may begin to email you the output of that command each time it's run, or it may be saved to a log file somewhere.
+The cron job you just created will run the command ``date`` at the top of
+every hour (e.g. at 10:00, 11:00, 12:00, etc.). Depending on how your system
+is configured, it may begin to email you the output of that command each time
+it's run, or it may be saved to a log file somewhere.
 
 A more in-depth example
 -----------------------
@@ -74,28 +101,40 @@ Let's look again at the example from before:
 
   05 12 * * 0 /home/jdoe /home/jdoe/jobs/copy-to-partition
 
-Let's dissect this a bit, as it will help when you're creating your own cron jobs. What is this output telling you? It is helpful to know what the fields of a "crontab" are. Here's a table with the order of fields, and their values:
+Let's dissect this a bit, as it will help when you're creating your own cron
+jobs. What is this output telling you? It is helpful to know what the fields of
+a "crontab" are. Here's a table with the order of fields, and their values:
 
   ====== ==== ========== ===== ========= ================
   MINUTE HOUR DAYOFMONTH MONTH DAYOFWEEK COMMAND
   0-59   0-23 1-31       1-12  0-6       filepath/command
   ====== ==== ========== ===== ========= ================
 
-.. note:: Order matters, and note that the first element is 0 for the minute, hour, and day of the week fields, while the day of the month and month fields begin at 1.
+.. note:: Order matters, and note that the first element is 0 for the minute, hour,
+  and day of the week fields, while the day of the month and month
+  fields begin at 1.
 
 Knowing this, we can see that this "crontab" means:
 
-  At 12:05 every Sunday, every month, regardless of the day of the month, run the command ``copy-to-partition`` in the ``/home/jdoe/jobs`` directory.
+  At 12:05 every Sunday, every month, regardless of the day of the month, run the
+  command ``copy-to-partition`` in the ``/home/jdoe/jobs`` directory.
 
-Let's take another example and create a cron job that checks disk space available every minute, every hour, every day of the month, every month, for every day of the week, and outputs it to a file named ``disk_space.txt``.
+Let's take another example and create a cron job that checks disk space
+available every minute, every hour, every day of the month, every month, for
+every day of the week, and outputs it to a file named ``disk_space.txt``.
 
 .. code-block:: console
 
   * * * * * df -h > disk_space.txt
 
-This would get us what we wanted (``df -h`` is the unix command for checking free disk space).
+This would get us what we wanted (``df -h`` is the unix command for checking free
+disk space).
 
-Field values can also be ranges. Let's say you want to edit this job to run the same command (``df -h``), but instead of running every minute, you only want the job to run it in the first 5 minutes of every hour, every day of the month, every month, for every day of the week. Run ``crontab -e`` again and changing the line to:
+Field values can also be ranges. Let's say you want to edit this job to run the
+same command (``df -h``), but instead of running every minute, you only want
+the job to run it in the first 5 minutes of every hour, every day of the month,
+every month, for every day of the week. Run ``crontab -e`` again and changing
+the line to:
 
 .. code-block:: console
 
@@ -106,7 +145,8 @@ will get you what you want.
 How do I remove a crontab?
 --------------------------
 
-Lastly, if you want to remove the command, again type ``crontab -e``, and then delete the line with that job in it from the file in your editor.
+Lastly, if you want to remove the command, again type ``crontab -e``, and then
+delete the line with that job in it from the file in your editor.
 
 To remove all cron jobs for the current user, type:
 
@@ -117,7 +157,8 @@ To remove all cron jobs for the current user, type:
 What are some common "cron expressions"?
 ========================================
 
-The "cron expression" syntax can be confusing to understand. Here are some common expressions to get you started.
+The "cron expression" syntax can be confusing to understand. Here are some
+common expressions to get you started.
 
 - ``* * * * *``: every minute
 - ``0 * * * *``: every hour, on the hour
@@ -142,29 +183,41 @@ Here is the standard "cron expression" cheat sheet [#]_::
     # |   |   |   |  |
     # *   *   *   *  *  command to be executed
 
-Put this template at the top of your crontab file so it'll be easy to remember what the fields do.
+Put this template at the top of your crontab file so it'll be easy to remember
+what the fields do.
 
 Notes on composing good "cron expressions"
 ------------------------------------------
 
-- If you want to run something every N hours, be sure to specify a minute expression (the first number) also; otherwise, the command will be run once a minute for the entire hour.
-- Commands run by **cron** won't have all of the configuration and environment variables that come from your shell initialization files (like ``.bashrc`` or ``.zshrc`` or such). In particular, make sure to specify the full path to your program if it's not in a commonly-used location like ``/usr/bin``.
+- If you want to run something every N hours, be sure to specify a minute
+  expression (the first number) also; otherwise, the command will be run once a
+  minute for the entire hour.
+- Commands run by **cron** won't have all of the configuration and environment
+  variables that come from your shell initialization files (like ``.bashrc`` or
+  ``.zshrc`` or such). In particular, make sure to specify the full path to your
+  program if it's not in a commonly-used location like ``/usr/bin``.
 
 Modify a specific user's crontab
 --------------------------------
 
-The ``crontab`` command can be used to view or modify a specific user's crontab file, instead of the current user's crontab file. For instance, to edit ``jsmith``'s crontab, type the following in a shell:
+The ``crontab`` command can be used to view or modify a specific user's crontab
+file, instead of the current user's crontab file. For instance, to edit
+``jsmith``'s crontab, type the following in a shell:
 
 .. code-block:: bash
 
   crontab -e -u jsmith
 
-This option also combines with the other options we looked at before (``-l`` for listing and ``-r`` for removing a user's crontab file).
+This option also combines with the other options we looked at before (``-l`` for
+listing and ``-r`` for removing a user's crontab file).
 
 Modifying crontab parameters
 ----------------------------
 
-With some cron implementations [#]_, you can add shell environment variables to the top of a crontab file that affect all of the commands run by those crontabs. For example, you could modify the ``PATH``, ``MAILTO``, ``HOME``, or any other variable.
+With some cron implementations [#]_, you can add shell environment variables to
+the top of a crontab file that affect all of the commands run by those crontabs.
+For example, you could modify the ``PATH``, ``MAILTO``, ``HOME``, or any other
+variable.
 
 --------