shell-init: error retrieving current directory: getcwd: cannot access parent directories: No such file or directory OR pwd: cannot get current directory: No such file or directory

Suddenly on my shell, in my vnc window, I got "shell-init: error retrieving current directory: getcwd: cannot access parent directories: No such file or directory" for any shell command I executed.


dragon:685> ls
shell-init: error retrieving current directory: getcwd: cannot access parent directories: No such file or directory
<op snipped>

Since it said "No such file or directory" , I tried executing "pwd" to get my current directory.  I got an error for "pwd" too..

dragon:736> pwd
pwd: cannot get current directory: No such file or directory


Puzzled..I did a "cd" .

dragon:737> cd

And then  executed "pwd". And Viola!! It worked!

dragon:738> pwd
/users/rover
dragon:739>

I later found out that I had deleted my "current working directory" in another shell window. When I did "cd" I got to my home directory and hence all my linux/unix commands worked..

Hope this helps!

How to set up cron job in linux

What is a cron job?

As a network admin, its very important that we know the use of the crontab command which is used to setup cron jobs.

Cron job are used to schedule commands to be executed periodically. You can setup commands or scripts, which will repeatedly run at a set time. Cron is one of the most useful tool in Linux or UNIX like operating systems. The cron service (daemon) runs in the background and constantly checks the /etc/crontab file, /etc/cron.*/ directories. It also checks the /var/spool/cron/ directory

crontab is the command used to install, deinstall or list the tables (cron configuration file) used to drive the cron daemon in Vixie Cron. Each user can have their own crontab file, and though these are files in /var/spool/cron/crontabs, they are not intended to be edited directly. You need to use crontab command for editing or setting up your own cron jobs.

To edit your crontab file, type the following command at the UNIX / Linux shell prompt:$ crontab -e

Syntax of crontab (Field Description)

Your cron job looks as follows for user jobs:

 
1 2 3 4 5 /filepath ag1 ag2
 

OR

 
1 2 3 4 5 /root/runscript.tcl
 

Where,

• 1: Minute (0-59)
• 2: Hours (0-23)
• 3: Day (0-31)
• 4: Month (0-12 [12 == December])
• 5: Day of the week(0-7 [7 or 0 == sunday])
• /filepath - Absolute path of the script or command name to schedule* * * * * command to be executed

Note: Only use absolute paths in the cron. Do not use relative paths.

EXAMPLE CRON FILE

       # use /bin/sh to run commands, no matter what /etc/passwd says
       SHELL=/bin/sh
       # mail any output to 'paul', no matter whose crontab this is
       MAILTO=paul
       #
       # run five minutes after midnight, every day
       5 0 * * *       $HOME/bin/daily.job >> $HOME/tmp/out 2>&1

       # run at 2:15pm on the first of every month -- output mailed to paul
       15 14 1 * *     $HOME/bin/monthly

       # run at 10 pm on weekdays, annoy Joe
       0 22 * * 1-5    mail -s "It's 10pm" joe%Joe,%%Where are your kids?%

       23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"

       5 4 * * sun     echo "run at 5 after 4 every sunday"

Permission denied: make_sock: could not bind to address

Permission denied: make_sock: could not bind to address

The other day when I was trying to bind httpd service (apache) on port 81,  I got an error saying "Permission denied: make_sock: could not bind to address" .

httpd: Could not reliably determine the server's fully qualified domain name, using 127.0.0.1 for ServerName

(13)Permission denied: make_sock: could not bind to address [::]:81

(13)Permission denied: make_sock: could not bind to address 0.0.0.0:81

no listening sockets available, shutting down

Unable to open logs

After a bit of debugging, found that the problem was with the policy that allows only favoured http ports.  

Use the semanage utility to find the ports.

1. semanage port -l | grep http 

http_port_t                    tcp      80, 443, 488, 8008, 8009, 8443

As you see , port 81 is not listed among the typical http ports

2. Add port 81 ( or any port of ur choice) to this list

semanage port -a -t http_port_t -p tcp 81.

3. Verify the port added

   

semanage port -l | grep http 

http_port_t                    tcp      81, 80, 443, 488, 8008, 8009, 8443

4. Restart httpd service. The service should start now!!

If you wish to remove a port from the favoured list , do as follows:

1. To remove port 81 ( added above) from the favoured http port list

semanage port -d -t http_port_t -p tcp 81

2. Verify whether the port is removed..

semanage port -l | grep http 

http_port_t                    tcp      80, 443, 488, 8008, 8009, 8443

Thats it!