Bash Shell: Check File Exists or Not

How do I test existence of a text file in bash running under Unix like operating systems?
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How To Use cat Command In Linux / UNIX

How do I use cat command in Linux? How do I use cat command in UNIX? How can I use cat command in UNIX or Linux shell scripts?
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Samba Restrict IPC$ ( list of shared resources )

The IPC$ share allows users to anonymously fetch a list of shared resources from a server. It can be used as a point of attack into a system. How do I disable or limit IPC$ under Samba to certain subnet such as 10.0.0.0/8?
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UNIX / Linux: Explain The Nine Permissions Bits On Files

Can you completely explain the nine permissions bits on UNIX or Linux files?
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psql: FATAL: Ident authentication failed for user "username" Error and Solution

Q. I’ve installed Postgresql under Red Hat Enterprise Linux 5.x server. I’ve created username / password and database. But when I try to connect it via PHP or psql using following syntax:

psql -d myDb -U username -W

It gives me an error that read as follows:

psql: FATAL: Ident authentication failed for user “username”

How do I fix this error?
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Display Apache Server Status with mod_status

Q. How do I display Apache server status such as current server activity and performance under Red Hat Enterprise Linux / UNIX / BSD?
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What Would Cause a Lot of ARP Broadcasts From One System / Machine

Q. I’m experiencing decreased network performance due to ARP broadcasts coming from one system. What would cause a lot of ARP broadcasts from one server / computer?
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