Centos

bugs

NFS mount permission denied

Error:

[root@traderdirect ~]# mount 10.93.138.18:/nfs-shares /mounts/tdstorage/
mount: 10.93.138.18:/nfs-shares failed, reason given by server: Permission denied

Solution: /bin/mount -t nfsd nfsd /proc/fs/nfsd See: this bug report

df and du do not match

When a disk is full but nothing shows up as taking up a lot of space (according to du) then it's possible files were deleted before they were closed.

To determine if this is the case, run this command: lsof 2>/dev/null | grep deleted then restart the offending process.

General

Add Swap

TO add a 4 gig swap:

• dd if=/dev/zero of=/swapfile bs=1M count=4096
• mkswap /swapfile
• swapon /swapfile

Then add the following to /etc/fstab:

• /swapfile swap swap defaults 0 0

Kernel Parameters for Oralce

• Put in /etc/sysctl.conf
• sysctl -a will list current parameters
• sysctl -p /etc/syscth.conf will reload new parameters

kernel.sem = 250 32000 100 128

net.ipv4.ip_local_port_range = 9000 65500
net.core.rmem_default = 262144
net.core.rmem_max = 4194304
net.core.wmem_default = 262144
net.core.wmem_max = 1048576
fs.aio-max-nr = 1048576

fs.file-max = 6815744

See more here

Changing hard & soft file limits

• Edit /etc/security/limits.conf

Ethernet Interface Details

[root@host ~]# ethtool eth0
Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
                                1000baseT/Full 
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
                                1000baseT/Full 
        Advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: g
        Wake-on: d
        Link detected: yes

Add EPEL Repo

• wget http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-4.noarch.rpm
• rpm -Uvh epel-release-5-4.noarch.rpm
• Edit /etc/yum.repos.d/epel.repo, add priority=3 to the end of the [epel] section

Check High Mem Usage

ps auxf | sort -nr -k 4 | head -10

Set up X11 Forwarding

• yum install xorg-x11-apps xorg-x11-xauth
• Verify X11Forwarding yes in /etc/ssh/sshd_config
• ssh -X hostname