Overview

In most Linux Distributions core file creation is disabled by default for a normal user. However, it can be necessary to enable this feature for an application (e.g. Oracle). For example, if you encounter an ORA-7445 error in Oracle, then it must be possible to write a core file for the user«oracle».

To enable writing core files you use the ulimit command, it controls the resources available to a process started by the shell, on systems that allow such control.

If you try to enable writing core files, usually you run in the following problem. Normally SSH is used to logon to the server.

ssh oracle@ora-server
$ ulimit -a

core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
file size               (blocks, -f) unlimited
pending signals                 (-i) 1024
max locked memory       (kbytes, -l) 32
max memory size         (kbytes, -m) unlimited
open files                      (-n) 65536
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 16384
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

Now, try (not as user root) to change the core file size to unlimited

$ ulimit -c unlimited
-bash: ulimit: core file size: cannot modify limit: Operation not permitted

Solution

1. Check Environment for ulimit

   The first step is to check, that you don’t set ulimit -c 0 in any shell configuration files for this user, for example in $HOME/.bash_profile or $HOME/.bashrc. Uncomment it if you have such an entry.

   #
   # Do not produce core dumps
   #
   # ulimit -c 0
    

2. Globally enable Core Dumps

   This must be done as user root, usually in /etc/security/limits.conf

   # /etc/security/limits.conf
   #
   # Each line describes a limit for a user in the form:
   #
   # <domain> <type> <item> <value>
   #
   *  soft  core  unlimited
    

3. Logoff and Logon again and set ulimit

   ssh oracle@ora-server
   $ ulimit -c
   0

   Try to set the limit as user root first

   su –
   ulimit -c unlimited
   ulimit -c
   unlimited

   Now you can set ulimit also for user oracle

   su – oracle
   ulimit -c unlimited
   ulimit -c
   unlimited

Perhaps the last step number 3 is not necessary, but we have figured out, that this is the way which always work. The core file size limitation is usually also set in different configuration files. If you want to enable cores, you can uncomment them.

In /etc/profile (Redhat)

# No core files by default
# ulimit -S -c 0 > /dev/null 2>&1

In /etc/init.d/functions (Redhat)

# make sure it doesn’t core dump anywhere unless requested
# ulimit -S -c ${DAEMON_COREFILE_LIMIT:-0} >/dev/null 2>&1

Now, from this current shell you can generate the core, so check ulimit before.

$ ulimit -a

core file size          (blocks, -c) unlimited
data seg size           (kbytes, -d) unlimited
file size               (blocks, -f) unlimited
pending signals                 (-i) 1024
max locked memory       (kbytes, -l) 32
max memory size         (kbytes, -m) unlimited
open files                      (-n) 65536
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 16384
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited