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Can’t re-open pipe to command substitution (fd 4): No child processes error and solution

Q. I’m running Debian Linux 64 bit server. I’m getting an error which read as follows:
Can't re-open pipe to command substitution (fd 4): No child processes

How do I fix the problem?

A. This error occurs when Linux server run out of open files maximum limit i.e system cannot create or open a new file due to number of open files reached the maximum limits of files.

To solve this problem just configure the system to accept the more open files. Please see previous faq:

Linux NFS Export / share directory to other UNIX / Linux computer

Q. I’m using CentOS 5 Linux 64 bit version. How do I share directory called /data2 to all other UNIX / Linux computers?

A. NFS (Network file system) is both a protocol and file system for accessing and sharing file systems across a computer network using UNIX and Linux. NFS v4 is used in modern Linux distributions. It offers performance improvements, mandates strong security, and introduces a stateful protocol etc.

How do I export a directory with NFS?

In order to export or share directory called /data2, you need to edit a file called /etc/exports. The file /etc/exports serves as the access control list for file systems which may be exported to NFS clients.:
# vi /etc/exports
Add config directive as follows:
/data2 *(rw,sync)

Each line contains an export point and a whitespace-separated list of clients allowed to mount the file system at that point. Each listed client may be immediately followed by a parenthesized, comma-separated list of export options for that client.


  • rw - Allow both read and write requests on /data2 NFS volume
  • sync - Reply to requests only after the changes have been committed to stable storage

Save and close the file. Restart the nfs service:
# /etc/init.d/nfs restart

NFS client configuration

Client computer need to mount file system using mount command or /etc/fstab file, enter:
# mkdir /mnt/nfs
# mount -t nfs4 nfsserver-name-or-ip:/data2 /mnt/nfs

Read the man page for more configuration options:
$ man exports