CoG uses system property UID to compose proxy name, see following comments in 
org/globus/common/CoGProperties.java:

 /**
     * Retrieves the location of the proxy file.
     * It first checks the X509_USER_PROXY system property. If the property
     * is not set, it checks next the 'proxy' property in the current
     * configuration. If that property is not set, then it defaults to a
     * value based on the following rules: <BR>
     * If a UID system property is set, and running on a Unix machine it
     * returns /tmp/x509up_u${UID}. If any other machine then Unix, it returns
     * ${tempdir}/x509up_u${UID}, where tempdir is a platform-specific
     * temporary directory as indicated by the java.io.tmpdir system property.
     * If a UID system property is not set, the username will be used instead
     * of the UID. That is, it returns ${tempdir}/x509up_u_${username}
     * <BR>
     * This is done this way because Java is not able to obtain the current
     * uid.
     *
     * @return <code>String</code> the location of the proxy file
     */
    public String getProxyFile() {
        String location;
        location = System.getProperty("X509_USER_PROXY");
        if (location != null) {
            return location;
        }
        location = getProperty("proxy");
        if (location != null) {
            return location;
        }
        return ConfigUtil.discoverProxyLocation();
    }



BUT, on AIX it doesn't have UID environment variable by default. It would- be
nice CoG can get uid in other way, like from output of "id -u" which can work
both on Linux and AIX.